Basic Structure of C Programming

Basic Structure of C Programming

            The format or way according to which a computer program is written is called the structure of the program. The program structure of different programming language is different. C is a structured programming language. It provides a well-defined way of writing programs.

            The basic structure of C program consists of the following main parts:

Preprocessor directives

ii) The main() function

iii) C statement

Preprocessor Directives

          The commands that given to instruction to the C-compiler are called preprocessor directives. They are given at the beginning of the source code. The preprocessor directives are also known as compiler directives. A preprocessor directive begins with a # sign followed by a word “include” or “define”. It does not end with semicolon (;).

            The preprocessor directives are processed before compiling the source code. The part of the C-compiler that takes action on the preprocessor directives is called preprocessor. For example, “include” directive is used to include header file in the C program.

            The most important preprocessor directives are as following:

Include directive

Define directive

The ‘include’

          The ‘include’ preprocessor directive is used to include the specified header file in the program. It means that this preprocessor directive tells the preprocessor to insert the definition of standard function into C program from a standard library.

            The syntax of “include” directive to include standard header file is as follows:

                        #include<name of header file>

For Example,

                        #include<stdio.h>

The ‘define’

            The define preprocessor directive is another important preprocessor directive. It is used to define a constant known as constant macro. A constant macro is an identifier, which is assigned a particular constant micro. The value of identifier remains constant during the execution of program.

            The general syntax of define directive is as follows:

                        #define identifier expression

For Example,

                        #define PI 3.1416

                        #define city Sialkot

Header file

            The header file contain the declarations or information of standard library function. These function are called in the main body of the program to perform different tasks. The extension of header file is “.h”.

            In C-Language, there are many header files. Each header file contain information for a specific group of function. For example, the header file “math.h” contain declaration of mathematical function available in C.

            A header file must be included at the beginning of the program, if its function are to be used in the program. A program may contain many header files.

The “include” preprocessor directive is used to include the header file into the program. The name of header file is written between angle brackets “< >” or in double quotes.

            The syntax to include a header file at the beginning of C program is as follows:

                        #include<name of header file>

For example,

                        #include<stdio.h>

                        #include<conio.h>

In most of C programs, header file “stdio.h” is used. The word “stdio” stand for Standard Input and Output. The scanf() and printf() function is most commonly used input and output and “conio.h” header file are use to “clrscr()”. It is also used to clear screen of monitor.

The main function

          The main() function indicates the beginning of the actual C-program. It is the point at which execution of program is started. When a C program is executed, the execution control goes to directly to the main() function.

            Every C program must have the main() function. The main() function comes after the preprocessor directives.

            The general syntax of main() function is follows:

            void main(void){

            Body of main() function

            }

The C Statement

            A program statement is a fundamental unit of any programming language. It is an instruction for the computer to do something. The set of statement of C program are written under the main() function between curly brackets i.e  { }. In C program , the library function are called for execution in the main body of the program. For example, the printf() function is used to display a message  or output of the program.

            Each statement of C program is terminated with semicolon (;). It is called statement terminator. If semi colon (;) is missing at the end of any statement , then the error message will be show by the C-compiler during compiling  process.

                        Statement missing;

Syntax of C-program is used to clear the computer screen and to display a message on the screen.

                        #include<stdio.h>

#include<conio.h>

main(){

clrscr();

printf(“welcome”);

}

Write a program to print your name

#include<stdio.h>

void main(){

printf(“My name is Zain”);

}