又是熟悉的c++四行题解

#include<bits/stdc++.h>
int main(){
    int n;std::cin>>n;if(n>=90)std::cout<<"A";else if(n>=80)std::cout<<"B";else if(n>=70)std::cout<<"C";else if(n>=60)std::cout<<"D";else std::cout<<"E";
}