C/Macro Preprocessor/if def

#define and #ifdef

<source lang="cpp"> //file1.h

1. define USD 1

//file2.h

1. define UKP 1

//file3

1. include <stdio.h>
2. include <file1.h>
3. if !defined (USD) || !defined (UKP)

   #error "RROR: NO_CURRENCY rate is specified."

1. endif

main() {

 int rs;
 rs = 10 * currency_rate;
 printf ("d\n", rs);

}

      </source>

#define, #ifdef #else example

<source lang="cpp">

1. include <stdio.h>
2. define TED 10

int main(void) {

1. ifdef TED

 printf("Hi Ted\n");

1. else

 printf("Hi anyone\n");

1. endif
2. ifndef RALPH

 printf("RALPH not defined\n");

1. endif

 return 0;

}

      </source>

Simple #if/#else example

<source lang="cpp">

1. include <stdio.h>
2. define MAX 10

int main(void) {

1. if MAX>99

 printf("Compiled for array greater than 99.\n");

1. else

 printf("Compiled for small array.\n");

1. endif

 return 0;

}

      </source>

Simple #if example

<source lang="cpp">

1. include <stdio.h>
2. define MAX 100

int main(void) {

1. if MAX>99

 printf("Compiled for array greater than 99.\n");

1. endif

 return 0;

}

      </source>