C Tutorial/Preprocessor/ifdef

ifdef

The ifdef directive makes substitutions based on whether a particular identifier is defined.

<source lang="cpp">#define USA 1 // #define EUP 1

1. include <stdio.h>
2. ifdef USA
3. define currency_rate 46
4. endif
5. ifdef EUP
6. define currency_rate 100
7. endif

main() {

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

}</source>

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