#include<bits/stdc++.h>
using namespace std;
int main()
{
    double x,y,z;
    cin>>x>>y>>z;
    double ans=x+y+z;
    if (ans>=200)
        cout<<fixed<<setprecision(1)<<0.8*ans;
    else
        cout<<fixed<<setprecision(1)<<0.9*ans;
    return 0;
}

#include<bits/stdc++.h> using namespace std; int main(){ double a,b,c; cin>>a>>b>>c; if(a+b+c>=200){ printf("%.1f",(a+b+c)*0.8); } else printf("%.1f",(a+b+c)*0.9); return 0; }

很简单的题，为什么没题解呢？（AC过了）

#include <bits/stdc++.h>
using namespace std;
int main()
{
    double a, b, c;
    cin >> a >> b >> c;
    double num = a + b + c;
    if (num >= 200)
    {
        cout << fixed << setprecision(1) << num * 0.8;
    }
    else if (num < 200)
    {
        cout << fixed << setprecision(1) << num * 0.9;
    }
    return 0;
}