Compile Error

rt,代码如下

#include <bits/stdc++.h>
using namespace std;
int t,n1,n2;
char op;
int main()
{
    cin>>t;
    while(t--)
    {
        string tmp;
        cin>>tmp;
        if(tmp[0]>='a'&&tmp[0]<='c')
        {
            op=tmp[0];
            cin>>n1>>n2;
        }
        else
        {
            sscanf(tmp.c_str(),"%d",n1);
            cin>>n2;
        }
        string x="";
        if(op=='a')
            sprintf(x.c_str(),"%d+%d=%d\n",n1,n2,n1+n2);
        else if(op=='b')
            sprintf(x.c_str(),"%d-%d=%d\n",n1-n2,n1-n2);
        else if(op=='c')
            sprintf(x.c_str(),"%d*%d=%d\n",n1,n2,n1*n2);
        cout<<x<<x.length()<<endl;
    }
    return 0;
}