/*===============================================*\

**	设计目的：简单计算器，计算形如10*(20.2-30.6)+5.0/2的表达式值

**	简要原理：中缀式转逆波兰式（后缀式）

**	IDE：Dev-Cpp 4.9.9.2

**	注意事项：括号必须是英文状态的

**	时间： 2014-6-17

\*===============================================*/

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#define maxn 1000

char buf[maxn], str[maxn], signStack[maxn], ch[2];

int len, id, idSign, idAns, i, n;

double ans[maxn];

void checkSign(char sign){

	if(sign == '(') signStack[idSign++] = sign;

	else if(sign == '*' || sign == '/'){

		while(idSign && (signStack[idSign-1] == '*' || signStack[idSign-1] == '/'))

			str[id++] = signStack[--idSign];

		signStack[idSign++] = sign;

	}else if(sign == ')'){

		while(signStack[idSign-1] != '(') str[id++] = signStack[--idSign];

		--idSign;

	}else{

		while(idSign && signStack[idSign-1] != '(') str[id++] = signStack[--idSign];

		signStack[idSign++] = sign;

	}

	str[id++] = ' ';

}

int check(double a, char sign){

	if(a == 0 && sign == '/'){

		printf("除数不能为0!，程序结束。\n");

		system("pause");

		exit(EXIT_FAILURE);

	}

	return 1;

}

double cal(double a, double b, char sign){

	switch(sign){

		case '+': return a + b;

		case '-': return a - b;

		case '*': return a * b;

		case '/': return a / b;

	}

}

int main(){	

	printf("\t\t\t\t简单计算器\n\n");

	printf("\t\t   ======================================\n");

	printf("\t\t  ||  支持+ - * / ( ) 等符号和负数输入  ||\n");

	printf("\t\t   ======================================\n");

	printf("\t\t\t\t\t\t原创作者：邱正钢\n");

	printf("\t\t\t\t\t\t完毕时间：2014年6月17日\n");

	printf("\t\t\t\t\t\tEmail：2276479303@qq.com\n");

	printf("请输入一个表达式，如 -10*(20.2-30.6)+5.0/2\n以回车结束:\n");

	do{

		gets(buf); id = idSign = idAns = 0;

		if((len = strlen(buf)) == 0) continue;

		int flag = 0; //这个是用来推断'-'字符是负号还是减号的。1表示数字，0表示 +*/(

		/*推断原理：假设第一次读取就碰到-，那么一定是负号，若近期一次读取是+*-/(那么

			也一定是负号，假设是右括号或数字那么是减号*/

		for(i = 0; i < len; ++i){

			if(buf[i] == ' ') continue;

			if(buf[i] >= '0' && buf[i] <= '9' || buf[i] == '.' || buf[i] == '-' && !flag){

				 str[id++] = buf[i]; flag = 1;

			}

			else {

				str[id++] = ' '; checkSign(buf[i]);

				if(buf[i] != ')') flag = 0;

				else flag = 1;

			}

		}

		while(idSign) str[id++] = signStack[--idSign];

		for(i = 0, n = 0; i < id; ++i){

			if(str[i] == ' ') continue;

			/*用添加空格的方式推断‘-’字符是负号还是减号，若‘-’后面挨着数字或小数点，那么一定是负号*/

			if(str[i] >= '0' && str[i] <= '9' || str[i] == '.' || str[i] == '-'

				&& (str[i+1] >= '0' && str[i+1] <= '9' || str[i+1] == '.')){

				sscanf(str + i, "%lf%n", &ans[idAns++], &n);

				i += n - 1;  continue;

			}else if(check(ans[idAns-1], str[i])){

				ans[idAns-2] = cal(ans[idAns-2], ans[idAns-1], str[i]);

				--idAns;

			}

		}

		printf("结果是 %.2lf\n", ans[0]);

		printf("输入Y 继续, N 退出: ");

		scanf("%s", ch);

	}while(ch[0] == 'Y' || ch[0] == 'y');

	printf("感谢您的使用！再见\n");

	system("pause");

	return 0;

}