Function Pointer. Not a good example.

fnptr.c

#include <stdio.h>

#define USE_BINARY_FUNC typedef struct { \
    T (*fn)(T, T); \
} T##_binfn;

USE_BINARY_FUNC(int)
USE_BINARY_FUNC(float)

int add(int x, int y) { return x + y; }
int sub(int x, int y) { return x - y; }
float mult(float x, float y) { return x * y; }

int main(void)
{
    int_binfn int_func;
    float_binfn float_func;
    
    int_func.fn = add;
    printf("%d\n", int_func.fn(3, 4));
    
    int_func.fn = sub;
    printf("%d\n", int_func.fn(3, 4));
    
    float_func.fn = mult;
    printf("%f\n", float_func.fn(1.1, 1.2));
    return 0;
}