拒绝switch，程序加速之函数指针数组

#include <stdio.h>
#include <time.h>

//加法
int add(int a,int b)
{
	return a+b;
}

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

//乘法
int multi(int a,int b)
{
	return a*b;
}

//除法
int divide(int a,int b)
{
	return a/b;
}

int claculate(int a,int b,char oper)
{
	//这里使用switch语句
	switch (oper)
	{
	case '+':
		return add(a,b);
	case '-':
		return subtract(a,b);
	case '*':
		return multi(a,b);
	case '/':
		return divide(a,b);
	default:
		return -1;
		break;
	}
}


void main()
{
	int a = 250;
	int b = 5;
	//统计程序运行时间
	clock_t start, finish; 
	start = clock();
	printf("%d\n",claculate(a,b,'+'));
	printf("%d\n",claculate(a,b,'-'));
	printf("%d\n",claculate(a,b,'*'));
	printf("%d\n",claculate(a,b,'/'));
	finish = clock();
	printf( "%f seconds\n", (double)(finish - start) / CLOCKS_PER_SEC );  
}

#include <stdio.h>
#include <time.h>

//加法
int add(int a,int b)
{
	return a+b;
}

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

//乘法
int multi(int a,int b)
{
	return a*b;
}

//除法
int divide(int a,int b)
{
	return a/b;
}



int claculate(int a,int b,int oper)
{
	//其实这里应该使用hashMap，将字符'+'映射到add函数。
	//直接使用数字是为了简便

	//声明指向函数指针的数组
	int (*pfunc[])(int a,int b)  = {add,subtract,multi,divide};

	return pfunc[oper](a,b);
}


void main()
{
	int a = 250;
	int b = 5;
	//统计程序运行时间
	clock_t start, finish; 
	start = clock();
	printf("%d\n",claculate(a,b,0));
	printf("%d\n",claculate(a,b,1));
	printf("%d\n",claculate(a,b,2));
	printf("%d\n",claculate(a,b,3));
	finish = clock();
	printf( "%f seconds\n", (double)(finish - start) / CLOCKS_PER_SEC );  
}