后缀表达式求值

 

#include
#include
#include
#include
#define MAXSIZE 30

typedef int ElemType;
typedef struct Stack{//栈结构
    ElemType data[MAXSIZE];
    int top;//栈顶指针
}Stack,*pStack;

void initStack(pStack S){//初始化栈
    S->top = -1;
}
bool push(pStack S,ElemType e){
    if(S->top == MAXSIZE-1){
        puts("栈满");
        return false;
    }
    S->data[++(S->top)] = e;
    return true;
}
bool pop(pStack S,ElemType *e){
    if(S->top == -1){
        puts("栈空");
        return false;
    }
    *e = S->data[(S->top)--];
    return true;
}
int main(void){
    char string[MAXSIZE];//存储字符串
    char tempNumber[MAXSIZE];//存储数值字符
    char ch;//分解每个字符
    int index;
    int number;//从字符中获得的数值
    int result = 0;//最终结果
    int count = 0;//数字计数
    int a1,a2;//辅助数值计算
    bool tag;//标志位，数字是否已经结束
    Stack numberStack;//数字栈
    pStack S = &numberStack;//指向栈的指针

    initStack(S);//初始化栈
    puts("Enter a string");
    gets(string);
    for(index=0;index
        ch = string[index];
        if(isdigit(ch)){
            tag = true;//现在输入的是数字
            tempNumber[count] = ch;
            count++;
        }
        else{
            if(tag){//判断上一个字符是不是数值
                tempNumber[count] = '\0';//一个数值结束了
                number = atoi(tempNumber);
                push(S,number);
                count = 0;//重新计算数值
                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;
}