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Basic of C

Atheendrh Kakkothatheendrh@gmail.comAtheendrh kakkoth

Execution of C Program

•Creating a program :An editor like notepad or word pad is used to create a C program. This file contains a source code which consists of executable code. save as .c

• Compiling the program :The next step is to compile the program. The code is compiled by using compiler. Compiler converts executable code to binary code

•Linking a program to library :The object code of a program is linked with libraries that are needed for execution of a program. The linker is used to link the program with libraries.

•Execution of program :The final executable file is then run by dos command prompt or by any other software.

TokensTokens are individual words marks in passage of text. In C, program the smallest individual units are known as C Tokens. C has Six types of Tokens. The Tokens are shown in figure

Tokens

• Keywords– These are reserved words of the C language. For example int, float, if, else, for, while etc.

• Identifiers– An Identifier is a sequence of letters and digits, but must

start with a letter. Underscore ( _ ) is treated as a letter. Identifiers are used to name variables, functions etc.

– Valid: Root, _getchar, __sin, x1, x2, x3, x_1, If

– Invalid: 324, short, price$, My Name

Tokens

• Constants– Constants like 13, ‘a’, 1.3e-5 etc.

• Strings– A sequence of characters enclosed in double

quotes as “…”. For example “13” is a string literal and not number 13. ‘a’ and “a” are different.

• Operators– Arithmetic operators like +, -, *, / ,% etc.– Logical operators like ||, &&, ! etc. and so on

Tokens

• special symbol: ~ ! @ # $ % ^ & * ( ) _ + { } [ ] - < > , . / ? \ | : ; " '

• White Spaces– Spaces, new lines, tabs, comments ( A sequence of

characters enclosed in /* and */ ) etc. These are used to separate the adjacent identifiers, kewords and constants.

Header file

Key word

IIdentifiers

Operators

Special symbol

Strings

Header file contains different predefined functions, which are required to run the program

Header File in C : Header file contains different predefined

functions, which are required to run the program. All header files should be included explicitly before main ( ) function

Assert.h Ctype.h Math.h

Process.h Stdio.h Stdlib.h

String.h Time.h Graphics.h

Followings are the some commonly used header files which plays a vital role in C programming :

Stdio.h

stdio.h refers to standard input/output header file. The functions which are declared in stdio.h are very popular.

scanf() -used to take input from the standard input stream

Printf() -prints to the standard output stream

Data Types in C :

Decision Making Statements

C program executes program sequentially. Sometimes, a program requires checking of certain conditions in program execution. These statements are called as 'Decision Making Statements' or 'Conditional Statements‘

• Followings are the different conditional statements used in C.

• If Statement• If-Else Statement

If Statement : This is a conditional statement used in C to

check condition or to control the flow of execution of statements.

Syntax:

if(condition) {

statements; }

If-Else Statement :This is also one of the most useful conditional

statement used in C to check conditions

Syntax: if(condition)

{ true statements;

} else

{ false statements;

}

Looping Statements A loop is used using condition. The repetition is

done until condition is true• Some common examples of this looping

statements are :• while loop• for loop

While loopIt is used to repeat a block of statements until

condition is true.

Syntax: while(condition) { statements; increment/decrement; }

For loop One of the most important feature of this loop is that

the three actions can be taken at a time like variable initilisation, condition checking and increment/decrement.

Syntax: for(initialisation; test-condition; incre/decre)

{statements;

}

#include <stdio.h> #include <conio.h> void main() { int a; for(i=0; i<=5; i++) { printf("\n"); }

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