int (*p[2])(int,int);

	p[0] = ∑ // address of sum() 
	p[1] = &subtract; // address of subtract()

#include "stdio.h"

int sum(int a, int b);
int subtract(int a, int b);  

int main(int argc, const char *argv[]){
	int (*p[2])(int,int);
	int result;
	int i = 2, j = 3, op;

	p[0] = ∑ // address of sum() 
	p[1] = &subtract; // address of subtract()

	printf("0: Add, 1: Subtract\n");	
	do {
		printf("Enter number of operation: ");		
		scanf("%d", &op);
	} while(op<0 || op>2);	
	result = (*p[op]) (i, j);	
	printf("%d", result);
	return 0;
}

int sum(int a, int b){
  return a + b;
}

int subtract(int a, int b){
  return a - b;
}