加减乘除法运算（函数数组指针法）

#include<stdio.h>

double add(double x, double y)//加
{
	return x + y;
}
double sub(double x, double y)//减
{
	return x - y;
}
double mul(double x, double y)//乘
{
	return x*y;
}
double div(double x, double y)//除
{
	if (y != 0)
	{
		return x/y;
	}
	else
	{
		printf("输入错误");
		return -1;
	}
}
void menu()
{
	printf("************************\n");
	printf("***1.add        2.sub***\n");
	printf("***3.mul        4.div***\n");
	printf("******* 0..exit ********\n");
	printf("************************\n");
}
int main()
{
	int input = 1;
	double a = 0;
	double b = 0;
	double ret;
	double(*p[5])(double a, double b) = { 0, add, sub, mul, div };
	while (input)
	{
		menu();
		printf("请输入需要的操作:\n");
		scanf("%d",&input);
		if (input > 0 && input <= 4)
		{
			printf("请输入操作数:\n");
			scanf("%lf%lf",&a,&b);
			ret = (*p[input])(a, b);
			printf("%.2lf\n", ret);
		}
		else if (0==input)
		{
			break;
		}
		else
		{
			printf("输入错误");
		}
	}
	return 0;
}