後綴表達式求值

 

#include<stdio.h>
#include<string.h>
#include<ctype.h>
#include<stdlib.h>
#define MAXSIZE 30

typedef int ElemType;
typedef struct Stack{//棧結構
    ElemType data[MAXSIZE];
    int top;//棧頂指針
}Stack,*pStack;

void initStack(pStack S){//初始化棧
    S->top = -1;
}
bool push(pStack S,ElemType e){
    if(S->top == MAXSIZE-1){
        puts("棧滿");
        return false;
    }
    S->data[++(S->top)] = e;
    return true;
}
bool pop(pStack S,ElemType *e){
    if(S->top == -1){
        puts("棧空");
        return false;
    }
    *e = S->data[(S->top)--];
    return true;
}
int main(void){
    char string[MAXSIZE];//存儲字符串
    char tempNumber[MAXSIZE];//存儲數值字符
    char ch;//分解每個字符
    int index;
    int number;//從字符中獲得的數值
    int result = 0;//最終結果
    int count = 0;//數字計數
    int a1,a2;//輔助數值計算
    bool tag;//標誌位，數字是否已經結束
    Stack numberStack;//數字棧
    pStack S = &numberStack;//指向棧的指針

    initStack(S);//初始化棧
    puts("Enter a string");
    gets(string);
    for(index=0;index<strlen(string);index++){
        ch = string[index];
        if(isdigit(ch)){
            tag = true;//現在輸入的是數字
            tempNumber[count] = ch;
            count++;
        }
        else{
            if(tag){//判斷上一個字符是不是數值
                tempNumber[count] = '\0';//一個數值結束了
                number = atoi(tempNumber);
                push(S,number);
                count = 0;//重新計算數值
                tag = false;
            }
            switch(ch){
                case '+':
                     pop(S,&a2);
                     pop(S,&a1);
                     push(S,a1+a2);
                     break;
                case '-':
                     pop(S,&a2);
                     pop(S,&a1);
                     push(S,a1-a2);
                     break;
                case '*':
                     pop(S,&a2);
                     pop(S,&a1);
                     push(S,a1*a2);
                     break;
                case '/':
                     pop(S,&a2);
                     pop(S,&a1);
                     push(S,a1/a2);
                     break;
                default:
                     break;
            }
        }
    }
    pop(S,&result);
    printf("%d",result);
    getchar();
    return 0;
}