Basic Structure of C Program

#include<stdio.h>

#include<conio.h>

void main ()

{

printf(“Hello World”);

}

It has two parts:

·         The preprocessor directive.

·         The main function.

Preprocessor directive:

            ‘# ‘indicates that is instruction for the compiler.

A preprocessor directive is always start with the symbol (#). In the above program ‘include’ is a preprocessor directive.

Many actions that is necessary for the program are not defined directly in a C program. In the above these action are defined in the form of functions in different libraries. Each library has a standard header file, which is referred to with .h extension.

‘stdio.h’ is a header file that contains standard input and output functions.

Types:

·         #include directive for defining identifiers from standard libraries.

·         #define directive for defining constant macros.

#include directive for defining identifiers from standard libraries:

Syntax:

                        #include<standard header file>

Examples:

                        Some examples of header files are:

#include<stdio.h>

#include<conio.h>

#include<math.h>

            The include directive tells the compiler where to find the meaning of standard identifiers (printf) used in t.he program. Theses meanings are described in files called standard input and output function.

#define directive for defining constant macros:

            Syntax:

                        #define  macro_name  expression

Examples:

            #define  PI  3.14

            #define  sec_mint   60

            Constant macro:

                        “Constant macro is a name that is replaced by a particular constant value before the program is sent to the compiler.”

The expression may be constant, arithmetic expression or a string. C preprocessor replace each occurrence of the identifier macro _name with value of expression. The value of macro_name can not be change during the program execution.

Function main:

            Main () is a function where the execution of the program are started. Every program has a main () function. It acts like a main gate of a house.

Main () is a starting point of program instructions. It is a entry point of the program.

The definition of the main function is always start with a reserved words (function return type) like (void, int , float and char) that are also  data types

Syntax:

            void main()

{

Body of main function

}

Void functions, also called non-value-returning functions, are used just like value-returning functions except void return types do not return a value when the function is executed. The void function accomplishes its task and then returns control to the caller.

Body of the function:

            It consists of C language statements, which are used to implement the program logic. It is enclosed in braces.

Delimiters:

After a main () function the instructions are written in the parenthesis {}. The rest of the lines of program form the body of the main function, the body is started by the opening parenthesis and end by the closing parenthesis.

Braces indicate the beginning and end of the function body. These braces are called delimiters.

 Statement Terminator:

            Every statement in a C++ program terminates with the semicolon (;). If any of the statement missing the statement terminator, the compiler will report an error.

Function printf:

            printf function is used to display the output of the program on the console screen.

Syntax:

            printf(“string”,variable1,variable2,……);

            printf(“string”);

            printf(variable1,variable2,………);

Example:

            printf(“Hello World”);