#include<bits/stdc++.h>
using namespace std;
int main()
{
freopen("jisuan.in","r",stdin);
freopen("jisuan.out","w",stdout);
double a,b;
char op;
cin>>op>>a>>b;
switch(op)
{
case'+':cout<<fixed<<setprecision(2)<<a+b;break;
case'-':cout<<fixed<<setprecision(2)<<a-b;break;
case'*':cout<<fixed<<setprecision(2)<<a*b;break;
case'/':cout<<fixed<<setprecision(2)<<a/b;break;
}
return 0;
}

https://www.cnblogs.com/cndarkmoon/articles/18216427
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