今天上数据结构，王老师讲的用栈实现算术表达式的值，晚上在实验室写了下，感觉自己的代码还是有问题（虽然还自己没有找到），感觉这个代码关于括号内运算符的优先级关系还是没有考虑好，这个代码也只是局限在10以内的加减乘除；先贴下代码，以后再来优化:

#include <iostream>

#include <stack>

#include <cstring>

#include <cstdio>

using namespace std;

stack<int> s2;

stack<int> s1;

char sign[4]={'+','-','*','/'};

char exp[110];

bool flag;

int cal(int a,int b,int c)

{

    if(c==0) return a+b;

    if(c==1) return a-b;

    if(c==2) return a*b;

    if(c==3) return a/b;

}

int solve()

{

    flag=0;

    int len=strlen(exp);

    exp[len]='#';

    len++;

    while(!s2.empty()) s2.pop();

    //s1.push(-1);

    int c=-1;

    for(int i=0;i<len;i++)

    {

        // cout<<exp[i]<<" ";

        if(s1.size()==0&&s2.size()==1&&i==len-1)

        {

            return s2.top();

        }

        if(exp[i]>='0'&&exp[i]<='9')

        {

            s2.push(exp[i]-'0');

        }

        else if(exp[i]=='(')

        {

            s1.push(4);

            flag=1;

        }

        else if(exp[i]==')'&&(c=s1.top())!=4)

        {

            s1.pop();

            int t1=s2.top();

            s2.pop();

            int t2=s2.top();

            s2.pop();

            int temp=cal(t2,t1,c);

           // cout<<temp<<"fgf ";

            s2.push(temp);

            i--;

        }

       else if(exp[i]==')'&&(c=s1.top())==4)

        {

            s1.pop();

            flag=0;

        }

        else

        {

            int j;

            if(!s1.empty()) c=s1.top();

            else c=-1;

            for(j=0;j<4;j++)

              if(exp[i]==sign[j])

                break;

             // cout<<j<<"  "<<exp[i]<<endl;

            if(flag&&j+5>c&&j<4) { s1.push(j);

              // cout<<c<<"  "<<j<<" df "<<exp[i]<<endl;

            }

            else if(!flag&&j>c&&j<4)

              s1.push(j);

            else

            {

            s1.pop();

            int t1=s2.top();

            s2.pop();

            int t2=s2.top();

            s2.pop();

            int temp=cal(t2,t1,c);

            s2.push(temp);

            //cout<<temp<<" fg ";

            i--;

            }

        }

    }

    return -1;

}

int main()

{

    while(scanf("%s",exp))

    {

        cout<<solve()<<endl;

    }

    return 0;

}