如题，代码如下：

#include <iostream>


using namespace std;

long long js(long long a,long long b,char op)
{
    if(op=='+')
    {
        return a+b;
    }
    else
    {
        return a-b;
    }
}

int main()
{
    long long nums[3]={};
    int flag,now=0;
    char op;
    char c;
    while(cin >>c)
    {

        if (c>='0' && c<='9')
        {

            nums[now]=nums[now]*10+(c-'0');

        }
        else if(c=='+' || c=='-')
        {
            op=c;
            now++;
        }
        else if (c=='=')
        {
            now++;
        }
        else if (c=='?')
        {
            flag=now;
        }

    }

    if(flag == 0)
    {
        cout << js(nums[1],nums[2],op=='+'?'-':'+') << endl;
    }
    else if(flag == 1)
    {
        cout << js(nums[2],nums[0],op=='+'?'-':'+') << endl;
    }
    else if(flag == 2)
    {
        cout << js(nums[0],nums[1],op) << endl;
    }


}

感谢