C function pointer

gistfile1.txt

#include <stdio.h>

int x2 (int n ) { return n*2; }
int x4 (int n ) { return n*4; }

int (*op[])(int) = {
    x2,
    x4
};

#define A(n) a##n

int main () {
	int a1  = 1;
	int a2  = 2;
	int a3  = 3;

	printf("%d\n", A(3));
	printf("%d\n", A(2));
	printf("%d\n", A(1));
}