The implementation of callback function in C.

callback.c

#include <stdio.h>
#include <stdlib.h>

void PrintTwoNumbers(int (*numberSource)(void))
{
        printf("%d %d\n", numberSource(), numberSource());
}

int overNineThousand(void)
{
        return (rand() % 1000) + 9001;
}

int meaningOfLife(void)
{
        return 80;
}

int main(void)
{
        PrintTwoNumbers(&rand);
        PrintTwoNumbers(&overNineThousand);
        PrintTwoNumbers(&meaningOfLife);

        return 0;
}