好难，写了大半个中午

#include<bits/stdc++.h> using namespace std; int main() { int a,b; char f; cin>>a>>b>>f; switch(f) { case '+':cout<<a+b;break; case '-':cout<<a-b;break; case '':cout<<ab;break; case '/':if(b==0) {cout<<"error!";return 0; } cout<<a/b;break; } return 0; }