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2010-03-17T09:31:00.001-07:00

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VISUAL BASICS

2010-03-17T09:26:00.001-07:00

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VISUAL BASICS

2010-03-15T10:00:00.001-07:00

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XML

2010-01-16T04:33:00.000-08:00

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ARTIFICIAL INTELLIGENCE :

2010-01-15T06:36:00.000-08:00

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2010-01-14T21:27:00.000-08:00

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2010-01-12T22:50:00.000-08:00

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2010-01-12T20:42:00.000-08:00

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2010-01-12T10:12:00.001-08:00

DATA STRUCTURES :

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C LANGUAGE

2010-01-12T09:33:00.000-08:00

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2010-01-12T08:59:00.000-08:00

1. Fundamental Data Type

8 Basic Data type defined by C are Character, Integer, Floating Point, Double Floating Point, Valueless, Booledan, Complex &Imaginary. First 5 of these are present in C89 while last three were added by new vesion of C99.Let discuss each of them in brief -

1. Character - Implemented by char keyword. They are used to store ASCII character and are always 1 byte long.

2. Integer - Implemented by int keyword. They are used to store integer value and are always 4 byte long.

3. Floating Point - Implemented by float keyword. They are used to store decimal values and are always 1 byte long.

4. Double Floating Point - Implemented by double keyword. They are also used to store decimal values but with higher precision and are always 8 byte long.

5. Valueless - Implemented by void keyword. They are used to explicitly define function returning no value or generic pointer. No variable of this type can be created.

6. Boolean - Implemented by _Bool keyword. They are used to store Boolean values ie. True or False and are always 1 byte long.

7. Complex - Implemented by _Complex keyword. They are used to store complex numbers and are operating system implemented.

8. Imaginary - Implemented by _Imaginary keyword. They are used to store imaginary number and are operating system implemented .

One important point worth mentioing here is that C only stipulates the minimum range of the data type and its size may vary according to system implementation. The range may increase but will never get below the standard value. Also if you want your program to be portable to maximum systems make use of compile type operator sizeof in your program and allocate memmory dynamically instead of using default memmory allocation.

2. Type Modifier

Type Modifiers are special keywords which can be applied to a data type to change their meaning to more precisely fit the special needs they need to attain. There are 4 type modifiers define in C - signed,unsigned,long,short.Below we discuss each of them one at a time.

signed - Can be applied to int and char. It changes the way the compiler interpret the variable. 1st data bit is assumed to be a sign bit. Integer is signed by default but character is unsigned. This modifier reduce the range to half of the maximum but allows to implement some algorithms efficiently.

unsigned - Can be applied to int and char. It changes the way the compiler interpret the variable. 1st data bit is assumed to be a data containg bit. Integer is signed by default but character is unsigned. This modifier increase the range to maximum (double of default) but cannot stored negative values.

short - Can be applied to int only. It enhances the portability of your program. Size of int is 16 bits (2 b ytes) minimum but on some system it may become 32 and even 64 reducing portability of your program. To make sure you int is always 16 bits it is recommended you use this modifier.

long - Can be applied to int and double. It enhances the portability of your program. Size of int is 16 bits (2 b ytes) minimum but on some system it may become 32 and even 64 reducing portability of your program. To make sure you int is always 32 bits it is recommended you use this modifier. Also when applied to double it increase the size from 64 bits to 128 bits, it doesnot increase the range but increase the digits of precision. It is biggest size default data type though there is a experimental and unstable data type in C99 long long double on 256 bytes but due to its implementation limits it is highly recommend you dont use it. Long double is sufficient for even high precision scientific values to large extent (unless you are calculation stars in the universe).

It is important to note that modifier cannt be applied to void or float. Also you are not permited to declare a void data type except generic pointers (which are internally int).

Also in case of int two different type modifiers can be simultaneously applied to further enhance the meaning.

Below is a list of data types with thier size and range -

char 8 Bits -127 to 127
unsigned char 8 Bits 0 to 255
signed char 8 Bits -127 to 127Bits
int 16 or 32 Bits Operating system based
unsigned int 16 or 32Bits Operating system based
signed int 16 or 32 Bits Operating system based
short int 16 Bits -32767 to 32767
unsigned short 16 Bits 0 to 65535
signed short 16 Bits -32767 to 32767
long int 32 Bits -2147483647 to 2147483647
signed long int 32 Bits -2147483647 to 2147483647
unsigned long 32 Bits 0 to 4294967295
float 32 Bits 1E -37 to 1E +37 Bits with six digits of precision
double 64 Bits 1E -37 to 1E +37 Bits with 12 digits of precision
long double 128 Bits 1E -37 to 1E +37 Bits with six digits of precision

One more point worth mentioning is default to int rule exisitng in C. Its obsolete now but some compilers do provide them to give backward comaptibility but its highly recomended you dont use them in any of your program. For curosity and knowledge sake it states that if a type modifier is written by itself then it will be assumed a modifier to a type int. In other words it means that -

signed A is interpreted as signed int A by Compiler.
unsigned A is interpreted as unsigned int A by Compiler.
short A is interpreted as short int A by Compiler.
long A is interpreted as long int A by Compiler.

Once again though int is implied it is a common practice to mention them anyway for sake of compatability.

3. Indentifier

Name of any user defined item item in c is called identifier such as functions, labels and variables.

Identifiers are of two types internal and external. Internal identifiers are one which have internal linkage meaning that they are known only internally in file such as local variables and static global variables. External identifiers are one which have external linkage meaning that they are known only outside their file such as function names and global variables.

In C identifiers can have any number of character but not all of them are significant.Significant characters are the character used to identify the identifier. For an identifier to be unique it must have name different by atleast 1 character from all other identifiers in the same scope. C89 specifies that atlest 6 characters of an external specifier and 31 characters of an external identifier be significant. C99 further relaxes this constraint stating that atlest 31 characters of external identifier and 63 characters of internal identifier must be significant. Though generally compilers make sure that a larger number of characters be significant but minimum number is always instated.

Names of identifier has to follow some rules -

1. They may contain only alphabets, digits and underscore, example Hi!!!, I.Love.You is incorrect.

2. They must start with an alphabet or underscore, example 1_Counter is an inavlid identfier.

3. They cannot be same as keywords because these are the words reserved from usage by C.

One important point is that your identifier can have same name as the function in the library but this may induce some serious error, especially if you include the header file with similar name function. In this case whenerever you refrence the function it will refer to your code function even when you desire to use the library function, simplest way avoid this bug to give your functions a different name.

It should be noted that c is type sensitive language that its identifiers are case dependent eg- C_ROCKS, C_rocks and c_rocks are all different identifiers in C.

Also it is recommended that you use a standard notation while naming the identifiers. Famous ones are hungarian notation and camel case notation. These standards while correctly applied can lead to many benefits such enhanced portability and maintainability. These factor gain importance as the size of the project increases.

4. Variable Overview

Variable referes to a location in memmory that can be used to a value that can be dynamically or statically modified by your program.

All variables must be declared before there are use, basic syntax is

; Example - unsigned int a ;

Above type modifier is optional.

Identifier used as variable name should comply with the rules stated above.

Varibles can be of three types -

1. Local

2. Global

3. Parameter

Each type has its own scope, limitation and function as discussed below.

5. Local Variables

Variables that are declared withn a function are local variable. They are also known as automatic variables but the term is obsolete.

Earlier local variables were declare using keyword auto butnow this keyword is implicitly applied as a result the use of this keyword in modern source code is virtually non exsistent but do keep it in mind if you encounter it in earlier codees.

Local variables have property that they can be accesed only in the code they are defined in. Code block starts with the { and ends with } ie. within a pair of curly brackets the code block exist.

Life span of global variables is for the period in which code block is executing. They get created when code block is entered and get destroyed when code block is left. They are stored on stack of your compiler which is a dynamic data storage which is the reason that local variables cannot retain their value. This property can be modified by static keyowrd, this is discussed below.

It is a rule in C that you must declare a local variable before using it. Also in C89 its a rule that all declaration of variables must be made before any executional statment of the code block bbut in C99 (like C++) it can be declared any where prior to its first refrence.

Note that two variables with same identifier (name) cannot be stored in same code block and would reslut an error by compiler, but same name local variables can exist in different code blocks and even aggregated code blocks (one inside another).

When the same name variables are used in different functions they bear no relation and doesnt know nor depend on other's existence.

When the same name variables are used in an agrregated code block, ie. one variable in outside code block and one in inside code block the inner one mask the outer one. After ineer code block ends the outer variable again comes into existence.

Following C Source code will help you grasp the detail of the topic -

#include

void f1 ()
{
int x = 10;
printf ("%d",x);// Outputs 10
}
void f2 ()
{
int x =20;
printf ("%d",x); //Outputs 20
}
int main ()
{
int x = 30;
{
int x = 40;
f1 ();
f2 ();
printf ("%d",x); //Outputs 40
}
printf ("%d",x); //Outputs 30
return 0;
}

6. Global Variable

Unlike local variable global variable are known throughout the program. They are declared outside all function and conventionally just after the include statements.

They should be use carefully and only when there is a defetive gain in performance or efficiency or they provide ease in programming. Most of the time they are used to stoe shared data but beautifully crafted programs also used them to store control information as control flags.

The major problem with global variables is that they lead to bugs which are very difficult to debugg and very easy to occur because the value of a global value can be easily modified by an undesirable side effect of your code. Also storage of global variable is on a fixed memory region which is non volatile for program life period. As a result a global variable always tend to bloack memory not only for a particular function execution but for entire program execution time as a result large number of global variables may overrun the memory allocated to your program leading to serious trouble. So global variables must be used when there is an absolute must.

A special situatuion occurs when global variable and local variable has same name. In this case the local variable mask the global variable and all refrences are made to it within its scope.

C Source Code below will clarify the situation -

#include

void f1 ()
{
int x = 10; //Outputs 10
printf ("%d",x);
}
void f2 ()
{
x =20;
printf ("%d",x); //Outputs 20
}
int main ()
{
int x = 30;
f1 ();
f2 ();
printf ("%d",x); //Outputs 30
return 0;
}

7. Parameter Variable

Parameter variables are used for passing values between functions. Value maybe control information or data.

They are very similar to local variables in a sense that they are dynamic and have life span of that of local variable. Even though they recieve paramet value they can act like a local variable and reassign values to the parameter variable.

Their main job is to get automatically intialize based upon the data passed.

C Source Code Illustrating formal parameters -

#include

void f1 (int x)
{

printf ("%d",x);//Outputs x
}
int main ()
{
int x = 30;
f1 (x*5);//Outputs 150
f2 (x+10);//Outputs 40
printf ("%d",x); //Outputs 30
return 0;
}

8. C Scopes

A visibilty of an identifier is determined by its scope. C defines 5 scopes which have a very fine yet important differences.

1. Global/Universal Scope - This scope is given to identifiers which are known through the project. Normal global variables and function names come under this scope.

2. File Scope - This scope is given to identifiers which are known only in the file they are declared. Staic global variables come under this scope.

3. Block Scope - This scope is given to identifiers which are known only in the code block they are declared. Local variables come under this scope.

4. Function Prototype Scope - This scope is given to identifiers which are known through a function to which they are passed as parameter. Parameter variables come under this scope.

5. Function Scope - This scope is given to identifiers which are known through thefunction. Labels identifier use to target goto statement come under this category.

Also there are three type of linkage defined in C which is very similar to scope -

1. External Linkage - Same as Universal Scope and is applied to global variables and function name.

2. Internal Linakge - Same as File scope and is applied to static global variables.

3.No Linkage - Combination of Block, Function and Function Prototype Scope and is applicable to local variables, parameters and labels.

These are rarely used terms which are used when the task of making fine distinction in identifier visibility is needed.

9. Type Qualifier

Type qualifiers in c are used to specify and contro the acess and modification of a variable. There are 3 type Qualifiers in C - const, volatile and restrict. They must precede the type name that they qualify. Each of type qualifier is discussed below in detail.

1. const - It is a very usefull keyword available to a cprogrammer but its usage is not that prevelant in comparison to potential and benefits its provides. const keyword provides many utility applicable to situtation they are applied.

When its applied to a varaible then value of variable cannot be modified by your program. They can be used as a constant. Also they can be intialized but after intialization there value is not changable by any software means.

When its applied to a pointer then the object its pointing to cannot be modified by the program. Though the value its pointing can be changed by other means but not by this pointers.

Situations you should use this keywords are special. This keywords can prevent bugs in your program by making sure that an essential constant value doesnot get modified as a side effect leading to incorrect result. This keyowrd is also applicable in situations in which you pass falue to a function by mean of pointers or in other terms call by refrence. In this case the function has the ability to modify input data in the original source. Now if you are pretty sure that you dont want this function to change your intial values you can pass the pointer as a constant pointer making sure that value pointed by that pointer cannot be modified.

For optimization purposes some compilers may also place the value in ROM so they are absolutely unmodifiable.

One elegnat example of use of const keyword is seen in standard library functions provided with C. All the parameter this function does not want to modify are declared as const. You should use the same approach as it will save you a lot of headache when the failure of your programs occur because of preventable bugs.

One very important point about const is that its value can be modified by hardware means (sometime desired, most of time undesired). This can also lead to bugs but its a very rare situatuion when some harware fault occurs such as memmory overflow etc. But using const keywords prevents modification by any software mean.

Its also well known fact that const keywords enhanced security of you software and also pose a mjor difficulty in reverse engineering processes.

2. volatile - This one of the rarest used C-Keyword and find special used in hardware dependent programs such as drivers or system clock based code. Its specifies that the variable can change without any implicit specification. In other words the variable value can change even if doesnot assign a new value by program.

This is neccesary because in order to optimizse the code the compilers change the order of evaluation or may even not check the new value of variable if they observe that the variable does not occur on left in any assignment statement. This feature can surely sabotage your hardware dependent code in which values changes automatically also at very high frequency. Using volatile keyowrd prevents this optimization and make sure complier check the value of the variable every time it is used.

Many programmers beleive that const and volatile are opposite of each other but in relaity they point to entirely diffrenet aspects. You can even use them on same variable, in this case it will specify the variable value changes dynamically but can only be accesed by your code as constant.

3. restrict - This is one of the newest features added to C. It is only available in C99.

Its only applicable to pointers.

It states that a restrict pointer is the only mean by which the data pointed to that object can be accesed. Data accesed from any other pointer is possible if and only if its based on the first one.

The major functionality it provides is that it enables the compilers to produce highly optimize code.

To programmers it provides a tool by which they can make sure that if a pointers is restrict it provides the sole access method to the data it is pointing.

Also one important deduction that can be made out that if two pointers are restrict they are pointing to entirely different data ie. the data they are pointing is non overlapping.

Like const , restrict keyword is also extensively used by the library function and users are recommended to use them to improve efficiency of their code.

The C source code below shows an simple application of type qualifiers -

#include

int main ()
{
const int x = 30;
cont volatile int * port = (const volatile int *) 0X1E;
int *restrict point = &x;
printf ("%d %d %d",x, *point, *port); //Outputs 30, 30, 30
return 0;
}

10. Storage Class Specifier

Storage class specifier when applied to variable tells the compiler how to store that variable. Storage class specifier always precede the varaible declaration. There are 4 storage class specifier defined in C. These are extern, static, register & typedef and are discussed in detail below.

1.extern - There are 3 general use of extern.

First , extern was once used before functions name to identicate the function has global scope but since now all the functions are automatically put into global scope this use is now virtually no existent.

Second use of extern is declaring that a global varible used in the file is from an external file. Though global variables have global scope they may be masked by variable of same identifier. Hence to make sure the global one is used we use external specifier. Also generally such declarations are made into header files and are specially usefull in programs splitted into many source files.

Third use of extern is most commonly used and enables a programmer to use a variable without defining by marking its declaration as extern. Some users may be confused by declaration and description so a brief description is appropriate. C defines that a varaible can have any number of declaration but only 1 definition. Declaration is the statement which tells the compiler what type of datat type that varible is such as statement int i; this statement only declares the code but doesnot define it. On other hand when you assign any value to a variable it get defined. In other words when first memmory is allocated the varaible is getting declared. If you intialize the variable while defining it you are declaring as well as defining in one statement. Extern just specifies that declaration of the variable is present but not in the same scope so compiler searches for it high and low for resolving this refrence.

The order in which refrence search is made is important.First the seacrch is made in bloack scope then in function scope then in file scope and in last universal scope. Compiler assumes that any definition which match the declaration first is the variable being refered to. In other words if variable definition is found in functions scope then C compiler doesnot search the file and universal scope. If no correct refrence is found then linker flanks an error message.

C Source Code showing use of extern is -

#include
int main (void)
{
extern int a;
printf ("%d" , a); // Displays 10;
return 0;
}
int a = 10;

2. static - This is a very high utility keyword and is frequently used in programming. The are applicable to user defined variables (except parameter) and have an entirely diffrenet effect when applied depending upon the scope of variable.

When applied to global variables its scope is limited to file only ie. other files included in the program has no clue of its existence. They provide a very powertool of hiding data and creating stand alone function because of which they are also used in library functions. The global variables of your stand alone function will be completely usefull in that program but are shielded from external effects when combined in a big program. The value of these variables can be modified only by the function in that source file and not outside it preventing bugs, mishandling and probably unauthorize access and program tempering.

When applied to local variables the variable is stored in global variable memmory space and not on stack. Even though the varaible has functions scope it does not get destroyed like local variable when function returns, instead it retains it value on next call. Static local varaibles are intialised only once on the first function call. They provide high functionality in certain algorithms. If they were not available global variables have to be used for them but this makes program ureliable because it is depending upon something thats outside it. In Software analysis term this increases programs coupling (dependence on others) and decreases there cohesion (Capability of work alone). It is just opposite of what we desire. Ideal module/subroutine is the one which has minimum coupling and maximum cohesion.

C Source Code Example below shows functionality of static keyowrd -

#include
static int callfunction;
void function (void)
{
static int a = 0;
a++;
printf ("Function have been called %d time",a);
}
int main ()
{
callfunction = 10;
for (int i = 0; i<callfunction;i++)
{
function ();
}
return 0;
}

3. register - This is a highly oeprating system and compiler dependent keyword. It is so dependent that it is allowed to a C compiler to even ignore them as if they never exsted and even then they will be complying with standards of C. Though on other c also states that this keyoword should be given prime importance where it is applicable.

A register variable is stored in CPU register instead of RAM and its a well known fact that there is nothing that provides faster access than CPU register. This register is very dynamic and also provided very very very limited space. Register are used by CPU for addressing RAM memmory but a register declared variable is stored in CPU register itself hence they prrovide very fast access to read and write.

Using a register keyword can make your program faster by many folds if properly used. CPU register are so limited that only 1-2 live variables can placed on it that also of non aggregate type (basic ones). So make sure you make only that variable register which have an drastic impact on the program, loop variables make excellent choice. Use register carefully keeping its limitation in mind at all times.

Also you dont have to worry about declaring too many variables register as compiler manage them for you but it doesnot decide on basis of impact on program, its your job and you have to tell compiler about them.

Also making a variable, a register variable is dependent upon many other constraints such as size of CPU registers, number of free registers with CPU, access to CPU register and much more so they are innately dependent on hardware and operating enviroment.

Following C Source code illustrates the use of registers -

#include

int main (void)
{
register int a;
for (a = 0; a < 10;a++)
{
printf ("%d", a); // Prints numbers 0 to 9

}
return 0;
}

4. typedef is a very contoversial storage class specifier because in actual it doesnt allocate storage neither defines or modify type of storage when applied to variable still it is defined in standard c under category of storage class specifier so we will discuss it here.

typedef keyword provides syntactic convienence. Using typedef we can rename a particular base data type. This doesnot create a new data type but only rename the base data type.

The name is not replacement but is addition and can be used again in a typedef expression to once agian create a new data type name of the original data type.

Typedef offers two advantages -

1. It makes your code portable since you are using your own name for the code generated by compiler for a particular enviorment, when you move to a new enviorment all you have to do is to modify the typedef statements according to the new enviorment and compile agian.

2. It creates a self documenting code, since new data names implies a closer meaning to reader who is reading than a basic data type name. This makes code easier to understand.

Read the C Source Code below to improve your understanding.

#include

int main (void)
{
typedef int age;
typedef age weight;

int a;
age b;
weight c;
return 0;
}
// Here all three variables a, b and c are of type int.

11. Intializing Variables

Intializing a variable is a process of declaring as well as defininf it. It is when a real memmory is allocated to it.

Basic intialization technique is using assignment operator, eg - int a = 0;

Multiple intialization technique eg - int a = 0, b = 10, c, d = 20;

Global variables and static local variables are intialized only once.

Local variables are intialized each time they are created or thier code block is entered.

Also unitialized static and local global variable are set to zero before thier prior use.

Uninitalize local variable contains undefined value (Random) before thier prior use.

Using an unitialized variable specially the local variables and pointers can lead to intense bugs which are even capable of entire system crash. To prevent this some compilers will indicate error but almost all of them will flank a warning to make sure it is not by a mistake (Some special cases such destroying a enemy computer this may find some good use but they are still unrelaible so study virus and trojan section, just kidding).

12. Constants

Constants refer to fixed values which your program cannot modify. They are also known as literals. You also make an varaible a constant by using const keyword as describe above. There are different types of constants including the a type from every basic data type. They can be broadly classified as data type constatns, base constants, string constants and back slash constants (escape sequences). We discuss each category below.

1. Basic Data Type Constants - All basic type have an constant associated with it. If not explicitly specified the c compiler allocates the minimum size data type to it capable of storing it but compiler also make sure it does not cross any type boundaries. One exception to previous statment is that the floating point value by default is double and not float even tough double has larger size. Below is all types of basic data type constants defined in C.

character - 'c'

multibyte character - 'cc'

wide character -L'c' or l'c'

int - 101

signed int - 101 (same as int as int is signed by default)

long int - 101L or 101l

unsigned int - 101u or 101U

float - 101.01f or 101.01F

double - 101.01

long double 101.01L or 101.01l

The character following the constants is called type suffix in c and is case independent.

2. Base Constants - As you probably knowing there are different number systems other than decimal, most improtant one among them is Hexadecimal and Octal Constants. Hexadecimal is a number system 0 - 16 while octal is number system 0-8. It is some time easier to use these special number systems than decimal specially while doing hardware programming through in which port values are Hexadecimal. Also they are usefull when you use them constatnly for some calculation, in this case you dont need to particulary feed equvalent decimal value to C because C provides automatic to and fro base conversion calculation. This is where base constant comes in telling compiler which base the value in the constant bleongs to a C then store its equvalent value in any internal way it prefers.Diffrent base constant are -

Decimal - 420

Octal - 0420 (starts with explicitly specified 0)

Hexadecimal - 0x420 (starts with explicitly specified 0x)

3. String Constant - String is a special type of constant which contains on more particluar sequence of characters. The characters are represented between double qoutes. Eg - "Hi".

4. Backslash Character constant or Esacpe Sequences - These are special characters defined in C to be used as character constant or in strings. They are used to write special characters which can not be written by keyboard in C. Various escape squence defined in C are -

\a alert or beep

\b Backspace

\f Formfeed

\r Carraige return

\n New Line

\t Horizontal Tab

\v Vertical Tab

\" Double Quotes

\C Octal Constant (where C is an Ocatal Constant)

\xC Hexadecimal Constant (where C is an Hexadecimal Constant)

\' Single Quote

// Backslash

\? Question mark

13. Operator Overview

Operators is a symbol used to relate two operands. When one or more such relations are combined we get an expression. C have highly developed and sophisticated set of operators providing the ability to programmer to do anything with maximum flexibility. Operators can be broadly classified into arithemtic, relational, logical, bitwise and miscellaneous. All the operators defined in c are discuss in subsequent topic in small related groups.

Operator can be of 3 types -

1. Unary opertor - accpets 1 operand. Eg - ++, -- , -

2. Binaryopertor - accpets 2 operand. Eg - +, - ,*, / ,

3. Ternary opertor - accpets 3 operand. Eg - ?

14. Assignment Operator

Assignment operator is used to assign values obtained from a expression to another variable. General form is

lvalue = rvalue;

here lvalue refers to left value and should be a modfiable variable.

rvalue refers to right value and should be a valid epression statement.

If automatic conversion is not possible in assignment type casting should be employed.

You can also use multiple assignements -

Eg- x=y=z= 0; this statement assign value zero to three varibles simultaneously.

There are also shorthand assignment operators/Compound Opertors which performs simultaneous task of assingment and arithemetic. These are += , -= , *= , /= , %=. These operands are always used whereever possible over thier expanded equivalent in a professionaly edited code.

For eg -

X += Y is equivalent to X = X+Y

X -= Y is equivalent to X = X-Y

X *= Y is equivalent to X = X*Y

X /= Y is equivalent to X = X/Y

X %= Y is equivalent to X = X%Y

15. Arithmetic Operator

Arithemetic operators do most of the basic arithemetic calculations. Artihemtic operators define in C are -

+ does addition Eg - 4 + 3 = 7

- does subtraction Eg - 4 - 3 = 1

* does multiplication Eg - 4 * 3 = 12

/ does division Eg - 4 / 3 = 1.333

% does modulus Eg - 4 % 3 = 1

- unary minus Eg - -(4) = -4

The result produce by these arithemetic operator is same as largest variable input ie. 4/3 = 1 , 4.0/3 = 1.33 , 4/3.0 = 1.33 & 4.0/3.0 is 1.33 . 4/3 is 1 because all constants in expression are int while in all other atleast one or more operand operated by opertor is float.

16. Increment and Decrement Operator

These are special arithemetic operators which are used to increase or lower the variable value by unity (1). Symbols for them are ++ (increment) and -- (decrement).

They should be used where possible because the code produce this way is more optimized specialy in case of linearly incremented code.

x+1 is equivalent to x++ or x--

x-1 is equivalent to x-- or x--

Though ++x and x++ and similarly x-- and --x employs same equivalent circuit they when used with assignment operator result into extremely diffrent result. The first form is called prefix and other one is called postfix form.The main difference is when assignment occurs with respect to increment or decrement.

Consider to variable x & y. Y having value 10 then in case

x = y++; x contains value 10 because increment is performed after assignemnt.

x =y++; x contains value 10 because increment is performed before assignemnt.

It should be noted that y is 11 in both cases.

17. Relational and Logical Operator

Relational operators used to calculate realtionship between variables while logical operators calculate the logic in these relationship. Since most of the times they are used together we will discuss them together.

They work on boolean data and produces boolean data. In C any 0 value is considered flase and any non-zero value (generally 1) is consider to be true. C99 also defines a data type _Bool which can store only two values true (1) or false (0).

Relational operators return 0 or 1 depending upon the validity of the condition they are checking. Various realtional operators defined in C are -

> Greater than

>= Greater than or equal to

< Less than

<= Less than or equal to

== equal to

!= not equal to

Logical operators return 0 and 1 by testing various logical relationship among themselves using logic properties. Various logic symbol in C are -

&& Logical AND

|| Logical OR

! Logical NOT

x y x&&y x||y !x
0 0 0 0 1
0 1 0 1 1
1 0 1 1 0
1 1 0 1 0

All other logic operator such as XOR , NOR, NAND can be implemented using combination of these operators.

Paranthesis as usual can be used to change their precedence.

Eg- ((3>4) && (2==1)) || ((4>3) && ~3 ) = ((0) && (0)) || (1 && 0) = 0

18. Bitwise Operator

C was intially designed to replace the assembly language and used for system programming such as driver designing and port maintainance. These devices innately contains the job of working with smallest element of storag bits and bytes. Bitwise operators defined in C provides this capability in which you can play with bits and bytes.

Relational operators are applicable to only char and int types. Various types of relational operator are -

& And, Used to logically and all the bits in the two operands and return the resultant output.

| Or, , Used to logically or all the bits in the two operands and return the resultant output.

^ XOR , Used to logically XOR all the bits in the two operands and return the resultant output.

~ Complement , Used to logically complement all the bits in a operand. Also using complement twice original result is produce.

<
>>n Shift right, Used to logically shift the bits in the operands n postion right and introduce zero from left and return the resultant output. The shift right bit is lost and cannot be returned.

Consider an example in which we work on char variable A (8bits) with value 7 in binary equivalent to 00000111 and B with value 13 with binary equivalent 00001101Then if

C= A & B then C = 00000101 => 5

C= A | B then C = 00001111 => 15

C= A ^ B then C = 00001010 =>10

C= ~A then C = 11111010 => 250

C= A>>1 then C = 00000010 => 2

C= A>>1 then C = 00001010 => 6

Truth Table For XOR -

x y x^y
0 0 0
0 1 1
1 0 1
1 1 0

One important point to note about bit shifting is that if A = B>>n bits then its is equivalent to B/n and if A = B<<n bits then its is equivalent to B*n as long as the bit lost in the shifting procdure is 0. If bit loss is 1 then there is a loss of data and this realtion does not hold true.

19. Question Mark Operator

Question Mark as name sugests is symbolize by ?. This is the only ternary operators in C. In other words this is the only operand which takes in three simulatenous inputs.

This operators major use is to replace an smal if then else statement.

Its general form is V = Exp1? Exp2 : Exp 3.

It means that Exp 1 is evaluated and if its true value of variable V is one obtained by solving EXP2 & if its false value of variable V is one obtained by solving EXP3.

Following C source code displays the use of Question mark operator-

#include

int main (void)
{
int x;
x = 1;
x = x>0 ? x : -x; // ternary operator used to find modulous
printf ("%d", x);
return 0;
}

20. Star and Ampercent Operator

Star operator is represented by * and Ampercent operator is represented by &. They are used in context with pointers which is the greatest all features in c. They are discussd in further tutorials.

Pointer is basically and address or memmory location of a variable.

* is used to reterive value from a location assuming that variable it is applied to store the memmory location to that value. It is also used in declaring pointers.

& is used to reterive adress of variable, it is used to retrieve the memmory location of that variable and this address is used as a feed to the pointers.

Though pointers are discussed in very minute details in further sections what follows is a C source code showing pointers in action -

#include

int main (void)
{
int source, target;
int *pointer;
source = 100;
pointer = &source;
target = *pointer
printf ("%d", target);
return 0;
}

21. Compile Time Operator

C only provides one compile time operator known as sizeof.

If sizeof is used efficeintly the object code produced by the compiler is precisely targeted to the enviorment and also your source code is extensively portable.

It is a property of sizeof that its value is determined at compile time and is dependent upon the hardware and operating system.

sizeof returns the size of the object passed to it as parameter in parenthesis. The value of size it return is a of type size_t which is some type of unsigned integer capable to returning maximum possible size.

As you know integer can be 16 or 32 or even 64 bit which can make your code very unportable a solution to the problem is to allocate memmory to the int variable dynamically depending upon the size of int variable in the enviorment usinf sizeof.

#include
#include

int main (void)
{
int* x;
x = (int *) malloc (sizeof (int)); // Use of sizeof to dynamically allocate memmory
*x = 1;
printf ("%d", *x);
return 0;
}

22. Comma Operator

Comma opertor as you cn guess is represted by ,

Comma operator is a operator with lowest precedence.

It is used to combine together several expression in one expression.

In comma operator all the expression on left evaluates to null and the rightmost expression becomes the value of the entire comma seprated expression.

The use of comma operator may be clear from following C source code -

#include

int main (void)
{
int x,y;
x = (y=4,y+3); // Used of comma operator to string two expressions.
printf ("%d %d", x,y);// Displays 7 and 4
return 0;
}

23. Dot and Arrow Operator

Dot operator is represented by . and arrow operator is represented by ->.

Both of these operators are used with union and structures which are discussed in detail in further sections. For brief knowledge Union & Structures are user defined aggregated data types. In strucutre each internal element has its own unique structure while in union they share

Dot operator is use to access or modify data from structure and union directly.

Arrow operator is use to access or modify data from structure and union using pointers.

Following C Source Code show the use of dot and arrow operator -

#include

struct data
{
int value1;
int value2;
}

int main (void)
{
data d1;
data* d2;
d1.value1 = 10;
d1.value2 = 20;
d2->value1 = 30;
d2->value2 = 40;
printf ("%d %d", d1.value1,d1.value2);
printf ("%d %d", d1->value1,d1->value2);
return 0;
}

24. Square Brackets and Parenthesis Operator

Square Bracket operator is represented by [ ] and Parenthesis operator is represented by ( ).

Square brackets is used to index Arrays. Arrays are discussed in details in further sections. In breif, arrays is collection of similar data types stored in sequential memmory locations of which each element can be accesed through an index.

Following C Source Code show the use of Square Bracket and Parethesis operator -

#include

int data [5]; // int array

int main (void)
{
int i, answer;
for (i = 0; i<5;i++)
{
data [i] = i; // Array indexing using square brackets with help of a loop
}
answer = ((data [0] + data [1]) * (data [2] - (data [3] % data [4]))) // Use of parethesis to modify precedence
printf ("%d", answer); // Displays -1
return 0;
}

25. Operator Precedence

When compiler parse the code it does some operators calculation earlier than others if order is different this may lead to a diffrent result to solve this problem compiler use a precedence table to decide which operator has to be solved first. This order can modified by parenthesis operator (( )) which has highest precedence. Higher precedence operator will calculated before lower precedence operator. Operators on same level can be solved either left to right or maybe reshuffled by compiler to produce optimize ouput.

Precedence of operators are as follow -

Highest :

( ) [ ] -> .

! ~ ++ -- - (type cast) * sizeof &

% / *

- +

<< >>

<= < > =>

== !=

&

^

|

&&

||

?

= += -= *= /= %=

,(comma)

26. Expression Evaluation

In a expression order of evaluation is decided by user by using parenthesis.

All subexpression that have to be solved on same level can be freely rearrange by compiler in any order to optimize code efficiency and some employ parsing them left to right but if you want a portable code you cannot make this assumption always true. This rearranging can also lead to some hard to find bugs which are caused by undesirable rearrangement and execution order. So as programmer it is your job to make sure that your code does not rely upon the execution subexpression. Situation can be described by the code below -

#include

int input = 10;

int f1 ()
{
input = input*5;
return input;

}

int f1 ()
{
input = input+ 10;
return input;

}

int main (void)
{
sum = f1 ()+ f2 (); // Unreliablity due to rearrangemet
//Any one of f1 () or f2 () can be executed first.
printf ("%d" , output); // Ambigious output (110,120)
}

27. Type Conversion

When variables and constatns of diffrent types are mixed in a single expression they all converted to same type.

General rule follow by the compilers is that all variables and constants are promoted to the largest type occuring in the expression this is called type promotion. Also result is return in this largest variable type.

Largest variable types are listed in decreasing order. If any operand is of not the largest type variable then next largest varible type is checked until the right one occuring in realation is found and then all the trems in that expresssion is - long double >> double >> float >> unsigned long int >> long int >>unsigned int >> int >> short int >> char

Type conversion may some time lead to loss of data when a bigger size type casted into smaller type the table shown below indicat possible cases for char.

Target Type Expression Type Possible Loss Of Data

char int(16) High Order 8 Bits
char int (32) High Order 24 Bits
char short int High Order 8 Bits
char long int High Order 24 Bits
char float High Order 24 Bits and preicision
char double High Order 56 Bits and precision
char long double High Order 120 Bits and precision
Similarly cases of all variables into other types can be calculated from their size

28. Type Casting

Type casting is an neccesary evil. C provides most of the automatic conversion between various compatible types but there may arise cases in which you dont want to use C's inbuilt type conversion or it is not capable of converting it. In this case you use a very powerfull tool know as type casting.

In C type casting allows you to convert a varible, constant or data of any type from any type. Casting leads to conversion atoccurs at binary level.

Its also a very dangerous things because when you do a unusal type casting you obtain a value in a variable which was never built to handle and when you used this variable there is on guessing what could happen. So be very very carefull while using type casting.

The genral syntax for typing casting when you have to convert a type1 into type 2 is

type2 variable = (type2) type1 variable.

Code below illustrates a simple type conversion -

#include

int main (void)
{
int a;
for (a = 0; a < 10;a++)
{
printf ("%f", (double) a/2); // Prints a float number even though variable is an int
}
return 0;
}

29. Expression Formatting

This very essential for a expression. You can create a unformatted expression code readable by compiler without any error but same code when read by somebody may literally throw him off and confuse it beyond limit.

You should use parenthesis to remove ambiguity from your expression.

Also spacing and tabiing should be added to expression to make it more readable.

Contray to general belie formatting does not have any beneficial or negative effect on your code. But proper formatiing can surely prevent headaches to you and anybody else trying to figure out the significance and meaning of the code. These formating are completely ignored by compiler. Some IDE also provides tool to automatically format the source code to a readble format. These tools are also available in stand alone form.

For eg - What is easy to read for a human even though both expressions are same

A = X/4-34*Y+2/2-7*9;

A= (X/4) - (34*Y) + (2/2) - (7/9);

As you are becoming a talented C Programmer reading these articles it is higly recommended you make a habit of proper formatting of expression as well ascoding.

2010-01-12T08:37:00.000-08:00

1. Flavors of C

C comes into 2 versions, C89 and C99.

The number after the alphabet represents the year in which the ISO/ANSI Standard for the language was adopted.

As you can guess, C89 standard was developed in year 1989 and C99 standard was adopted in C89 also includes the features added to the language in year 1995 as Amendment 1.

C99 is superset of C89. That means all the features available in C89 are also available in C99. This is generally true but there is some incompatibilities in both the versions and C99 discard some obsolete features of C89.C99 mainly expanded C89 by adding new innovative features and huge numeric libraries.

In all tutorials clear distinction between C89 and C99 will be maintained as knowing difference between C89 and C99 is part of being a top notch programmer.

Although C99 added many Innovative features you would like to restrict your code only to C89 because even though a lot of time has passed since C99 was release the C compilers available for C have still not incorporated it into their structure. Its C89 code which most C compilers are able to compile. C89 is also widespread language than C99 and generally considered to be C.Also the famous language C++ is formed from C89 so you will not able to compile C99 code on a C++ Compiler even though you can use it to compile a C89 code.

2. History of C

C was invented by Dennis Ritchie and first implemented by him on a DEC PDP – 11 based on a Unix O.S.

C was influence by a language called B which was invented by Ken Thompson.

First book ever written on C was ‘The C Programming Language’ by Dennis Ritchie and Brian Kernighan.

First standard of C was adopted in 1989 by ANSI/ISO.

An Amendment was added to C language in year 1995.

Second standard of C was adopted in year 1999 by ANSI/ISO.

3. ISO/ANSI Standard

ISO stands for International Standard Organization

ANSI stands for American National Standard Institute.

For many years de facto standard of C was provided with UNIX but as the variety of systems and O.S. increased each of the provided its own version of C language. This became big problem as many variant of same language came into existence simultaneously, creating a chaos. Then came ANSI/ISO organizations which standardize the C language and every variant has to obey these standards hence most general and essential part became common to all.

Standard created a programming syntax and library (set of functions) which every compiler of C language was compulsory to include.All the compilers presently contain complete standard C and much more. As standard C is very limiting, for example no graphics or interrupts access function are defined in standard C but your compiler will be having them for sure because they form an essential part of programming.

Last point to mention is that if you want your code to portable to large number of operating systems and compilers you should restrict your code to standard C.

4. Middle Level Language

All the programming languages are divided into 3 levels

High Level Language
Middle Level Language
Low Level Language
High Level Languages – These languages are more oriented to be user friendly and syntax nearly approaches English. They have poor efficiency and flexibility.

Low Level Languages – These languages are computer or machine oriented. They allow programmer to code with maximum efficiency and flexibility but coding is quite tough. Its syntax nearly approaches the binary language.

Middle Level Language – The middle level languages is one which combines best feature of both high and low level languages. They are easy to code as well as efficient and flexible.

C is a middle level language.

Example –

High Level – Basic, Pascal, COBOL, FORTRAN

Middle Level – C, C++, Java, C#

Low Level – Assembly Language

5. Portability

Portability means by definition means that ability to adapt code written one programming environment onto another.

In Laymen terms it means that if you compile or designed a program in Windows and wish to run it in Linux or Dos and it does run then code is said to be portable in the two environments and can be use interchangeably without any code modification.

Low Level Language code is not portable generally while its easy portable for High Level Language.

Code generated by C is also very portable even though it has its limitations which should be kept under consideration. This not a disadvantage keeping in mind that c allows us to do system level programming. That is it gives us the ability to modify bits, bytes, and words the basic identities through which a computer operates.

To make your code most portable you must restrict it to Standard C.

6. Structured Language

C is a structured Language.

It represents the philosophy of programming use such as Block-Structure in FORTAN and OOP (Object Oriented Programming) in C++.

The main feature of Structure Language is compartmentalization of code.

This philosophy allows C to handle far more complexity than its predecessors. C can easily handle code up to 10000 lines.

Compartmentalization of code means ability of one section of code to completely hide itself from other section of codes.In C Compartmentalization of Code is achieved by deploying subroutines. Each subroutine is a stand alone code. It’s completely separate from other subroutines. It takes input data as parameters, process them, do its job and return the result as output. As a result no side effect is caused the program.

It also facilitates the reusability of code as same code could be used in variety of programming situations and could be easily inserted into another program.

C does not have a strict field concept this means that you can place code anywhere on a line.In C end of programming line is made by a semicolon.

Structure languages support many loop constructs such as for, do, while etc and use of goto generally discouraged in structure language while goto form a very essential part of a non structured language such as FORTAN, COBOL and Basic.

Structure Language also have concept of library. Library consists of large number of subroutines and can act as building blocks of a program. These blocks acts like bricks which when cemented together can form a huge skyscraper.

This programming approach is also called a top - down approach. In this main algorithm is broken in to small parts and each part is coded separately.

In nutshell Structure programming approach give programmer capability to code an algorithm efficiently, clearly with elegance and conceptualize true meaning of the algorithm.

7. Compilers Vs. Interpreters

There are two general ways a program can be converted from source code into object code it can be compiled or interpreted.

In layman terms it can be call the ways through which an code can be converted into a computer readable format from a human readable format.

Generally a programming language is designed keeping in mind one of the above methodologies. For example you can say that Java was designed to be interpreted and Pascal for compilation.

C was designed for Compilation.

Irrespective of design any language can be compiled or interpreted but efficiency can vary in both processes for same code.

Compiler and Interpreter main difference is in the way they read your source code.Interpreter reads source code one line at a time and then convert it to respective object code while compiler reads source code completely in one reading and convert it into respective code.

A compiler takes more time in conversion than an interpreter.

A Compiled program runs faster than a interpreted program.

8. Object Code Vs. Source Code

The Programming code created by the user is known as source code.

The Programming code generated by the Complier\Interpreter is known as object code.

Source Code is in human readable format.

Object Code is in computer readable format.

Source Code is Input to a Compiler\Interpreter while object code is Output of a Compiler/Interpreter.

Source Code is in Text Format While Object code is in Binary Format.

9. Compile Time Vs Runtime

Compile Time is the time for which program is compiled.

Run Time is the time for which program is interpreted.

Static Programming is done at compile time while dynamic programming such as DMA (Dynamic Memory Allocation) is done at Runtime.

10. Linker

In general all c compilers come with a library which includes standard library and much more. You use this functions more frequently than any thing else.

In general when compiler come across a reference of library function in your code while compiling it remembers its name and leave a space holder for its code.

Now when Compilation is complete it’s the job of a linker to link the object code of your program with object code of library functions.

These functions object code are in relocatable format and real physical memory is allocated to them only by compiler. Initially only offset Information is stored.

Linker is also used in process of separate compilation in this program have subroutines spread over more than one file. Each of these files are separately compiled and its linker’s job to resolve unknown references.

Linker can be stand alone , with the compiler or provide by you Operating System.

11. Integrated Development Environment (IDE)

Integrated Development Environment is the in thing. It is combination of editor, Linker, Compiler and interpreter in one big bundle software.

Programs are quickly developed in these IDEs. They provide shortcut to every function and you don’t have to leave even one window.

Otherwise you would be writing a program in notepad, compiling it on command line and then linking it an then executing the compiled result to find the output and so on. This could pretty cumbersome.

Also debugging that is finding errors in a program is also quite easy in an IDE.

There are many IDEs available on net I would recommend Turbo C++ 3.0. It is one of the oldest compilers yet the interface it provides for learning is unbeatable even by the most recent compilers. It is a dos based compiler and the one on which budding programmers should start their programming experience.

Turbo C++ 3.0 also provides BGI graphics which are now obsolete, yet are most effective in learning Games or 3D Programming because of their easy syntax.

12. Role of main

Like jigsaw puzzle, made up of many pieces, C Program is made up of one or more functions.

For a function to be validly compile function that must be present should be main (). It is the entry point of your program or in other words the first function to be compiled by your program.

In general main forms an outline of the program formed by function calls. The functions can call more functions or even themselves by process of recursion.

Main can also be code to accept arguments from command line which we will be discussing in future tutorials.

General form of main is –

int main ( ) // Avoid using void main( )
{
f1 ( );
f2 ( );
……
return 0;
}

13. Keywords

Keywords are some words reserved by C. They when combine with C Syntax forms C Programming Language.

There are 32 keywords in C89 and 37 keywords in C99. C99 adds five new keywords to the original language.

C89 Keywords –

auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if, int, long, register, return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while.

Additional C99 Keywords –

_Bool, _Imaginary, restrict, _Complex, inline.

You cannot have identifier name same as a c keyword that is why they are called reserved words.

Also try not to name your identifiers as library functions or as main otherwise it may lead to a name collision.

One point worth mentioning is C is Case-Sensitive that is in this upper case and lower case are considered to be different this means go is a keyword while GO is not.

14. Standard Library

You can easily write program from just keywords but that would have very limited capabilities as C provide no keywords for input/output, graphics etc.

In C this achieved with help of Library functions. Every compiler comes with a gigantic library completely covering standard library and this library is the real power of C.

You would be relying on this library for almost everything in your program.

Standard Library has more or less 180 functions under 24 header files which form the backbone of c programming language. You can find detailed reference of each of the program inour C Standard Library Section.

15. Memory Map

A compile C program generates 4 memory regions which it uses during its life time.

Stack
Heap
Global Variables
Program Code
Stack is used for many purposes such as holding local variables, program state, function calling and much more.

Heap is a region of free memory which can be used by your program through Dynamic Memory Allocation.

Global Variables refer to the data you have put I global namespace and they retain their identity till program terminates.

Program Code is your object; in this memory region it is stored.

16. C and C++

They most common question newcomers asked are what relation between C and C++ ?

C++ is superset of C. It means C++ incorporates entire C language with some minor incompatibilities.

You can use a C++ compiler to compile C code but you should ensure that file extension .c not .cpp. This extension tells a C++ compiler to do C compile on your source code.

17. Why learn C?

Well why learn C this most important topic in this website so here is a little article I wrote a while ago to clear your doubts permanently.

10 Reasons - Why C Should Be Your First Programming Language

To a beginner programmer the biggest question is where to start. Which language to choose from the mighty pool of 100's of languages.
This is was the same question I asked myself when I started writing my first program. I tried many languages but finally I came to C, the most beautiful and charming language of all. I was literally blown away by the simplicity and elegance of C.
Though C is simple it is one of the most powerful languages ever created.
In this dynamic IT world new language come every day and get obsolete, so there must be something in the C which has remained there for 3 decades and more and even today there is hardly any language which can match its strength.
90% of the starting programmer says that C has been superseded by its predecessors such as C++, Java, and C # and so on so why learn C. I don't know why they think so but I know one thing that they will never excel the other 10% programmers who differs from this opinion. Simple reason is how could a skyscraper building stand against time if its foundation is not strong.
Now Let us begin to analyze reason why C should be your first programming language.

1. I believe nobody can learn C++ or Java directly. To master these languages you need to have a strong concept of programming element such as polymorphism, classes, inheritance etc. Simple question is how you can learn such complicated concepts when you don't even know about the basic elements such as block functions. C is a language which begins from scratch and it has foundational concepts on which today concepts stand on.
2. It is language on which C++ is based on, hence C# also derive its origin from the C. Java is also a distant cousin of C and share the same programming concept and syntax of C. These are the most dominant languages in the world and all are based on C. To rock the world through them you must get rocking with C.
3. C++, Java, and C # make use of OOP (Object Oriented Programming). Not all programs need it even though it is a powerful tool. Such programs are still written in C.
4. When ever it comes to performance (speed of execution), C is unbeatable.
5. Major parts of the Windows, Unix and Linux are still written in C. So if you want program these OS or create your own you need to know C.
6. Device drivers of new devices are always written in C. The reason is that C provides you access to the basic elements of the computer. It gives you direct access to memory of your CPU through pointers. It allows you to manipulate and play with bits and bytes.
7. Mobiles, Palmtops, PDA's etc are gaining popularity every second. Also appliances such as T.V., Refrigerators, and Microwaves etc. are becoming an integral part of our daily needs. You may not know but they have a CPU with them which do need programming and the software's written for them are known as embedded system programs. These programs have to be fast in execution but also have a very little memory. No question why C is ideally suited for embedded system programming.
8. You must have played games on your PC. Even today these astounding 3D games use C as their core. Why? The simple reason who will play the game when it takes a lot of time fire a bullet after you have given command from the console. The reply to the command should be damn prompt and fast. Reply in 1 Nano second is an outstanding game; Reply in 10 Nano seconds is crap. Even today there is no match for C.
9. C is a middle level language. There are three types of language - High Level, Middle Level & Low Level. High level languages are user oriented, giving faster development of programs, example is BASIC. Low level languages are machine oriented; they provide faster execution of programs. C is a middle level language because it combines the best part of high level language with low level language. It is both user and machine oriented and provides infinite possibilities.
10. Last but not least it is a block structured language. The first symbol of a modern language is that it is block structured. Each code exists in separate block and is not known to code in other block providing easy means of programming and minimizing the possibilities of undesirable side effects. C is designed from the base to top to be a block structured language. Many older languages, most popular being BASIC tried to introduce this concept but their short coming can never fulfilled as they were never built along these line.
I think I have given all reason I know why c should be your first programming language. One thing is for sure that there no other language which more reliable, simple and easy to use.

C LANGUAGE :

2010-01-11T10:02:00.001-08:00

Introduction

What is a high-level language? Why is C unusual?

Any sufficiently complex object has levels of detail;
the amount of detail we see depends on how closely we scrutinize the object.
A computer has many levels of detail.

The terms low level and high level are often used to
describe these layers of complexity in computers.
The low level is buried in the computer's microchips and microcircuits.
The low level is the level at which the computer seems most primitive and
mechanical,
whereas the high level describes the computer in less detail,
and makes it easier to use.

You can see high levels and low levels in the workings of a car.
In a car, the nuts, bolts, and pistons of the low level
can be grouped together conceptually
to form the higher-level engine.
Without knowing anything about the nuts and bolts,
you can treat the engine
as a black box: a simple unit that behaves in predictable ways.
At an even higher level
(the one most people use when driving),
you can see a car as a group of these black boxes,
including the engine,
the steering, the brakes, and so on.
At a high level, a computer also becomes a
group of black boxes.

C is a high-level language.
The aim of any high-level computer language is to provide an easy,
natural way to give a list of instructions
(a computer program) to a computer.
The native language of the computer
is a stream of numbers called machine language.
As you might expect,
the action resulting from a single
machine language instruction is very primitive,
and many thousands of them can be required
to do something substantial.

A high-level language provides a set of instructions
you can recombine creatively
and give to the imaginary black boxes of the computer.
The high-level language software will then
translate these high-level instructions
into low-level machine language instructions.

Thats The Introduction :)

BASIC BATCH FILE PROGRAMMING :

2010-01-11T07:28:00.000-08:00

Hiii Friends :

This is Rakesh.J

Juz wanna tel u al about

The Basics Of Batch File Programming.

'Coz I know only the Basics... :-)

1.INTRODUCTION :

Anywayz... Now, What is a Batch File ?

Batch file is just a series of commands

written in Notepad or any text editor

with an extension " bat ".

We can give any number of commands

in the batch file programming...

except the syntax must be correct.

You might be thinking that

what these commands might be!

Dont worry by looking at the words

like " syntax " and " commands "...

These are not the Big Structural Commands

and Syntaxes of a

" C " program or " Java " or

what ever be the other languages one!

These are just the commands of

a normal command prompt.

You can find all these commands

in the command prompt by just..

Opening the command prompt and

tying " help " under...

Simple??

Thats the Beauty of a Batch File Programming...

You can also edit ant batch file,

By just right clicking it and clicking " edit "

It gives a Great Programing Xperience

with a just few number of steps...

Lets start making a batch file... :-)

2.MAKING A BATCH FILE:

To make a batch file,you just open a note pad

enter the commands,

and when saving it,give the extension as ".bat".

that is,"yourfilename.bat" instead of

"yourfilename.txt".

I would give you one example..

Creating A Batch File By Batch File Programming :

Go to start menu

Open "run" type "notepad"

and ur notepad is opened.

Simply type "logoff.exe" in your notepad

Close it and save it, with the extension of "bat"

To be clear, the text file must be

"logoff.bat" or any other "yourwish.bat"

As simple as eating a banana....

(Banana is one of my favorite fruit :-)

Yes, you have created a batch file,

what now?

How to use it?

Just go to your batch file and double click on it...

You would see your system logging off!!

Isn't cool??

If yes learn more....

Create a batch file to copy a file from one folder to another

For answer verification comment me with ur email id...

For assistance and more information on

batch file programming mail me at...

" http://innovationdelightes@gmail.com "

3.WORKING :

Yeah... Fine....

I think now you are able to make

small batch file programs...not that too small:-)

But,have u thought how the stuff works???

Well,I will tell you...

The moment you double-click on any batch file,

the command prompt gets initialized and

The commands which you have given,

gets executed line by line...

The command prompt first executes

the command of first line

and then goes to second line.. and so on...

If the syntax of the commands given are correct,

The file would give you the appropriate result...

But if it gets under the wrong syntaxed commands,

like we normally do!;

The prompt gets terminated and gives you the result..

Upto the correctly syntaxed commands...

Got it???

Thats how a batch file works...

Why staring at that thing so seriouisly??

Go now,and create a batch file to shutdown your PC...

For help,type "help shutdown"

in your command prompt...

Be aware of the options of shutdown...

It wont work without the options...!

Mail Me To Know More about Batch Filing..

innovationdelightes@gmail.com

4.BATCH FILEing IN DETAIL :

Are you satisfied with it?? No?? Well, me either!

Okay now Im going to tell you the

whole batch file(ing) in detail....

Lets start with an example... as I always do...

Okay, I will give you some useful example.....

I think you all be knowing where

the temp files are stored

and to delete them timely...

Lets start now...
Open your notepad....

Type "cd.." - to change the current directory..

Then, "c:" - to get in to c drive..

The command:" del /Q c:\windows\temp\*.* "

- to delete all files(not folders) from temp directory of windows

Immediately," del /Q c:\windows2\prefetch\*.* "

- to delete all files from prefetch

Finally,"del /Q "c:\documents and settings\"your user name"\

local settings\temp\*.*" - to delete from %temp%

exit - to exit...

So, your note pad should look like this...

cd..

c:

del /Q c:\windows2\temp\*.*

del /Q c:\windows2\prefetch\*.*

del /Q "c:\Documents and Settings\your user name\

localsettings\temp\*.*"

exit

( Of course, Not in Red Color :-) )

And finally save the file with extension "bat"

after closing it... Hurray!! Your batch file is created...

Now double click on it and see the magic...

Check all temporary files if there in your system...

No Files??? That was successfully done...

Those are the Basic Temp folders...

To Know all the temp folder and

wanna delete them, Watch the video down there... :-p

Did you noticed 4 things here?? Did you???

1).The command "del"...

2).The option "/Q"...

3).The " " marks for only the 5th line command

4).Last, the " *.* " ..

1) " del " is the command to delete files...

2).The option "/Q" is given to

delete these files forcibily...

If this option is not given,

the prompt asks for confirmation (y/n) to delete the files..

3).The " " marks are given only to the

5th command. This is because,in the adress,

(Documents and Settings\username\local settings)

contains spaces...

So our Brother prompt does not considers

them as spaces if the marks " " are not given

Hence it takes as

(DocumentsandSettings\username\localsettings\) and

searches for the folder...

(Ofcourse, it doesnot finds them either!)

So, the cotation marks " " are given to them...

Hence, by giving the marks " " the prompt considers

it as a whole string and executes the command.

4).The " *.* " notation! It indicates

the prompt which files to delete.

If you give the command " del /Q c:\a\*.bat ",

it 'Q'uietly deletes all bat files

from the folder c:\a (if present any!)

If you give the command

copy c: \ a \ any . * d : \ b,

It would copy all files with name "any" having

any extension from c:\a to d:\b

And thats how it works...

Finished learning???

Go now and make a batch file to copy

all files of extension ".exe" from c:\windows

and paste them to any folder

You got it???

Really did you get it by yourself???

No??? Mail Me and I wud send u the answer :-)