C - Preprocessors #Ifndef #Endif - ifndef

Learn C - C tutorial - Ifndef - C examples - C programs

C Preprocessors #ifndef #endif - ifndef - Definition and Usage

#ifndef exactly acts as reverse as #ifdef directive.
If particular macro is not defined, “If” clause statements are included in source file.
Otherwise, else clause statements are included in source file for compilation and execution.
#endif’ always matches the nearest ‘#ifdef’ (or ‘#ifndef’, or ‘#if’).
Also, we cannot start a conditional group in one file and end it in another.
The number of necessary #endif directives changes according to whether the elseif or #else directive is used.

C Syntax

 #ifndef identifier

#endif

#endif’ always matches the nearest ‘#ifdef’ (or ‘#ifndef’, or ‘#if’).
Also, we cannot start a conditional group in one file and end it in another.
The number of necessary #endif directives changes according to whether the elseif or #else directive is used.

C Syntax

 #endif newline

Sample - C Code

#include<stdio.h>
#define wikitechy 
void main()
{
    #ifndef  wikitechy
    printf( "Hello! welcome to wikitechy world\n" );
    #define wiki
}
#else
    printf( "www.wikitechy.com\n" );
#endif
}

C Code - Explanation :

In C programming #include<stdio.h> specifies a statement which tells the compiler to insert the contents of stdio at that particular place. A header file is a C file, that typically ends in ".h".In this example, #define wikitechy defines the constant name WIKITECHY.
In this example, #ifndef wikitechy specifies the reverse of #ifdef directive.
#define wiki specifies the directive, there by executing the #else statement.

The command #else specifies the else statement and prints the statement www.wikitechy.com.
In this example, #endif specifies the end of the program.

Sample Output - Programming Examples

Here in this output the “www.wikitechy.com” is printed in the console window since the #else directive has been defined.

UP NEXT IN C

View More Quick Examples

C Basics

Operator in C

Preprocessor Directives in C

Get Put in C

If Statement in C

C Programming Functions

Dynamic Memory Allocation in C

File Handling in C

Related Searches to C Preprocessors Ifndef Endif

c 言語 ifndef ifndef c 言語 ifndef debug ifndef em c ifndef system verilog c if endif preprocessor statements define if statement c 言語 endif why and when do we use the define directive define if statement in c what does endif mean if endif in c preprocessor directives in c preprocessor directives what are preprocessor directives c preprocessor directives preprocessor directives in c programming preprocessor directives in c language preprocessor directives c c programming preprocessor directives preprocessor directives in c examples list of preprocessor directives in c what are preprocessor directives in c types of preprocessor directives in c use of preprocessor directives in c what is preprocessor directives preprocessor directives in c with examples

C - Preprocessors #Ifndef #Endif - ifndef