Computer system

#include<stdio.h>

#include add.c

void main()

{

void add(); //FUNCTION PROTOTYPE/ DECLARATION.

add(); //FUNCTION CALLING

}

The file add1.c contains the function definition as follows.

void add()

{

int a,b,c;

printf(“enter two numbers”);

scanf(%d%d”,&a,&b);

c=a+b;

printf(“c value is:%d”,c);

}

3 : CONDITIONAL COMPILATION DIRECTIVES : C preprocessor also supports number
of conditional compilation directives as



1 : #undef : Undefined a macro

2 : #ifdef : Tests for a macro definition.

3 : #endif : Specifies the end of #if.

4 : #if : Tests compile-time condition.

5 : #else : Specifies alternative when #if test fails.

These are used to select a particular segment of code for compilation depending on the
condition.

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,EXAMPLE PROGRAM FOR CONDITIONAL COMPILATION DIRECTIVES:

A) EXAMPLE PROGRAM FOR #IFDEF, #ELSE AND #ENDIF IN C:

 “#ifdef” directive checks whether particular macro is defined or not. If it is defined, “If”
clause statements are included in source file.

 Otherwise, “else” clause statements are included in source file for compilation and
execution.

Ex:

#include <stdio.h>

#define RAJU 100

int main()

{

#ifdef RAJU

printf("RAJU is defined. So, this line will be added in " \

"this C file\n");

#else

printf("RAJU is not defined\n");

#endif

return 0;

}

OUTPUT:

RAJU is defined. So, this line will be added in this C file



B) EXAMPLE PROGRAM FOR #IFNDEF AND #ENDIF IN C:

 #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.

C PROGRAMMING Page 192

, Ex:
#include <stdio.h>
#define RAJU 100
int main()
{
#ifndef SELVA
{
printf("SELVA is not defined. So, now we are going to " \
"define here\n");
#define SELVA 300
}
#else
printf("SELVA is already defined in the program”);

#endif
return 0;

}
OUTPUT:

SELVA is not defined. So, now we are going to define here

C) EXAMPLE PROGRAM FOR #IF, #ELSE AND #ENDIF IN C:

 “If” clause statement is included in source file if given condition is true.

 Otherwise, else clause statement is included in source file for compilation and execution.

Ex:

#include <stdio.h>
#define a 100
int main()
{
#if (a==100)
printf("This line will be added in this C file since " \
"a \= 100\n");
#else
printf("This line will be added in this C file since " \
"a is not equal to 100\n");
#endif
return 0;
}


OUTPUT:
This line will be added in this C file since a = 100

C PROGRAMMING Page 193