cca is called from the command line.
In the following examples, foo.c is the following:
main(){ #ifndef FOO #define FOO 1 int foo_temp = FOO; printf("FOO = %d\n", foo_temp); #else int bar; scanf("%d", &bar); #endif /* FOO */ printf("Hello, world!\n"); #ifdef N #if N == 42 printf("The ultimate answer is 42\n"); #elif N == 13 printf("Boy are you unlucky.\n"); #else printf("This number isn't very interesting.\n"); exit(); #ifndef TIME printf("You are out of TIME.\n"); #endif /* TIME */ #endif /* N == 42 */ #else #define N 7 int n = 7; printf("We all know n = %d\n", n); #endif /* N */ }