跳转表实例

/* 用跳转表实现简易计算器 */

#include<stdio.h>   
#include<string.h> 
#include<stdlib.h>  

#define NUM 10 

double add(double a, double b)  
{
	return a+b;
}

double sub(double a, double b)  
{
	return a-b;
} 

double mul(double a, double b)  
{
	return a*b;
} 

double divide(double a, double b)  
{
	return a/b;
}

double compare_max(double a, double b)
{
	return (a>b)?a:b;
}

double compare_min(double a, double b)
{
	return (a<b)?a:b;
}

int search_keyword( char const * const desired_word, char const *keyword_table[])
{
	char const **kwp = NULL;

	/* 遍历指针数组，查找想要的操作符 */
	for(kwp = keyword_table; *kwp != NULL; kwp++)
	{
		/* 找到操作符后，返回它在指针数组中的位置 */
		if(strcmp(desired_word, *kwp) == 0)
			return (kwp - keyword_table);
	}

	return -1;
}

/* 定义指针数组，用作存储关键字的表。在表的末尾加上NULL指针，则查找时无需知道表的长度。 */
char const *oper_sequence[] = {"add", "sub", "mul", "divide", 
"compare_max", "compare_min", NULL};

/* oper_func是个数组，其中元素的类型是函数指针，函数返回值是double类型 */
double (*oper_func[])(double, double) = {add, sub, mul, divide, 
compare_max, compare_min}; 												

int main()  
{
	char oper[NUM] = {0};
	int seq = 0; 
	double data1 = 0;
	double data2 = 0; 
	double result = 0;

	printf("Operator:");
	/* 将输入的操作符存入oper数组 */
	scanf("%s", oper);

	seq = search_keyword(oper, oper_sequence);
	/* 没有找到对应的操作符时的错误处理 */
	if(seq < 0)
	{
		printf("Operator not found.
");
		return -1;
	}

	printf("请输入参数data1,data2:");
	scanf("%lf,%lf", &data1, &data2);

	result = oper_func[seq](data1,data2);
	printf("result is: %f
", result);
	
	return 0;
}