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cmacrosc-preprocessorpreprocessor-directive

Is it possible to compute factorial value of a proprocessor value during compile time in C?

#define num 7  \\ user can change this
#define size ????  \\I want this value (factorial of num) to be computed during compile time

int array[size][num];

I want to define array globally, but its size is dependent on preprocessor num's value. So I want the value (factorial of num) to be determined at compile time.

Is it possible? if yes, how?

Solution

  • In a separate .h file (for example fc.h):

    #if num == 1
#define sum 1
#elif num == 2
#define sum 2
#elif num == 3
#define sum 6
#elif num == 4
#define sum 24
#elif num == 5
#define sum 120
#elif num == 6
#define sum 720
#elif num == 7
#define sum 5040
#elif num == 8
#define sum 40320
#elif num == 9
#define sum 362880
#else
#error wrong number
#endif

    Usage

    #define num 7
#include "fc.h"

int array[sum][num];