堆栈入门-简单计算器

#include <stack>
#include <stdio.h>
#include <ctype.h>
using namespace std;
char str[220];
int mat[][5]={
                1,0,0,0,0,
                1,0,0,0,0,
                1,0,0,0,0,
                1,1,1,0,0,
                1,1,1,0,0,
                };
stack<int> op;
stack<double> num;
void getOp(bool &reto,int &retn,int &i){
    if(i==0 && op.empty()){
        reto=true;
        retn=0;
        return;
    }
    if(str[i]==0){
        reto=true;
        retn=0;
        return;
    }
    if(str[i]>=‘0‘ && str[i]<=‘9‘){
        reto=false;
    }
    else{
        reto=true;
        switch(str[i]){
            case ‘+‘:retn=1;break;
            case ‘-‘:retn=2;break;
            case ‘*‘:retn=3;break;
            case ‘/‘:retn=4;break;
        }
        i+=2;
        return;
    }
    retn=0;
    for(;str[i]!=0 && str[i]!=‘ ‘;i++){
        retn*=10;
        retn+=str[i]-‘0‘;
    }
    if(str[i]==‘ ‘)i++;
    return;
}
int main(){
    while(gets(str)){
        if(str[0]==‘0‘ && str[1]==0)break;
        bool reto;
        int retn;
        int idx=0;
        while(!op.empty())op.pop();
        while(!num.empty())num.pop();
        while(true){
            getOp(reto,retn,idx);
            if(reto==false)num.push((double)retn);
            else{
                if(op.empty() || mat[retn][op.top()]==1)
                    op.push(retn);
                else{
                    double tmp;
                    while(mat[retn][op.top()]==0){
                        double a,b;
                        b=num.top();num.pop();
                        a=num.top();num.pop();
                        switch(op.top()){
                            case 1:tmp=a+b;break;
                            case 2:tmp=a-b;break;
                            case 3:tmp=a*b;break;
                            case 4:tmp=a/b;break;
                        }
                        op.pop();
                        num.push(tmp);
                    }
                    op.push(retn);
                }
            }
            if(op.size()==2 && op.top()==0) break;
        }
        printf("%.2f\n",num.top());
    }
    return 0;
}