/*===============================================*\
** 設計目的：簡單計算器，計算形如10*(20.2-30.6)+5.0/2的表達式值
** 簡要原理：中綴式轉逆波蘭式（后綴式）
** IDE：Dev-Cpp 4.9.9.2
** 注意事項：括號必須是英文狀態的 
** 時間： 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("除數不能為0!，程序結束。\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簡單計算器\n\n");
 printf("\t\t ======================================\n");
 printf("\t\t || 支持+ - * / ( ) 等符號和負數輸入 ||\n");
 printf("\t\t ======================================\n");
 printf("\t\t\t\t\t\t原創作者：邱正鋼\n");
 printf("\t\t\t\t\t\t完成時間：2014年6月17日\n");
 printf("\t\t\t\t\t\tEmail：2276479303@qq.com\n");
 
 printf("請輸入一個表達式，如 -10*(20.2-30.6)+5.0/2\n以回車結束:\n"); 
 do{
 gets(buf); id = idSign = idAns = 0;
 if((len = strlen(buf)) == 0) continue;
 
 int flag = 0; //這個是用來判斷'-'字符是負號還是減號的。1表示數字，0表示 +*/(
 /*判斷原理：如果第一次讀取就碰到-，那么一定是負號，若最近一次讀取是+*-/(那么
 也一定是負號，如果是右括號或數字那么是減號*/
 
 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;
 /*用增加空格的方式判斷‘-'字符是負號還是減號，若‘-'后面挨著數字或小數點，那么一定是負號*/
 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("結果是 %.2lf\n", ans[0]);
 printf("輸入Y 繼續, N 退出: ");
 scanf("%s", ch);
 }while(ch[0] == 'Y' || ch[0] == 'y');
 printf("感謝您的使用！再見\n");
 system("pause");
 return 0;
}