HDU_1237_简单计算器

运算符为+，-,*,/；操作数为整数；且没有括号

设定符号优先级，先在栈底压运算符0

#include<iostream>
#include<cstdio>
#include<cstring>
#include<stack>
using namespace std;

stack<int> op;
stack<double> num;

char input[205];

bool prio[][5]=
{
    1,0,0,0,0,    //0
    1,0,0,0,0,    //+
    1,0,0,0,0,    //-
    1,1,1,0,0,    //*
    1,1,1,0,0,    //,/
};

void getNext(bool &isOp,int &opNum,int &loc)
{
    if('0'<=input[loc]&&input[loc]<='9')
    {
        int tmp=0;
        while(input[loc]!=' '&&input[loc]!=0)
        {
            tmp*=10;
            tmp+=input[loc]-'0';
            loc++;
        }
        isOp=0;
        opNum=tmp;
        if(input[loc]!=0)
            loc++;
    }
    else
    {
        isOp=1;
        if(input[loc]==0)
            opNum=0;
        else if(input[loc]=='+')
            opNum=1;
        else if(input[loc]=='-')
            opNum=2;
        else if(input[loc]=='*')
            opNum=3;
        else
            opNum=4;
        loc+=2;
    }
}

int main()
{
    while(gets(input))
    {
        while(!op.empty())
            op.pop();
        while(!num.empty())
            num.pop();
        if(strlen(input)==1&&input[0]=='0')
            break;
        bool isOp=0;
        int opNum=0,loc=0;
        op.push(0);
        while(loc<=strlen(input))
        {
            getNext(isOp,opNum,loc);
            if(isOp==0)
                num.push(opNum);
            else
            {
                int opTop=op.top();
                if(prio[opNum][opTop]==1)
                    op.push(opNum);
                else
                {
                    while(prio[opNum][opTop]==0) //这个地方之前出错，当当前运算符优先级比栈顶元素低，应该一直计算至栈顶元素优先级低于当前元素优先级
                    {
                        double num2=num.top();
                        num.pop();
                        double num1=num.top();
                        num.pop();
                        int nowOp=op.top();
                        op.pop();
                        opTop=op.top();
                        if(nowOp==1)
                            num.push(num1+num2);
                        else if(nowOp==2)
                            num.push(num1-num2);
                        else if(nowOp==3)
                            num.push(num1*num2);
                        else if(nowOp==4)
                            num.push(num1/num2);
                    }
                    op.push(opNum);
                }
            }
        }
        printf("%.2f
",num.top());
    }
    return 0;
}