#include <bits/stdc++.h> 
using namespace std;
int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    cout << a * 0.2 + b * 0.3 + c * 0.5;
    return 0;
}

没啥可说的了，看注释吧

#include <bits/stdc++.h>
using namespace std;
double a,b,c;
int main()
{
int sum=0;
cin>>a>>b>>c;
a=a*0.2;//50%=100分之50=10分之5
b=b*0.3;//30%=100分之30=10分之3
c=c*0.5;//20%=100分之20=10分之2
sum=a+b+c;
cout<<sum;
return 0;//完美结束
}

```

```

习惯性写函数

#include<bits/stdc++.h>
using namespace std;
int homework,test,examinstion;
int mark(int a,int b,int c)
{
    int sum = 0;
    sum = a*0.2 + b*0.3 + c*0.5;
    return sum;
}
int main()
{
    cin>>homework>>test>>examinstion;
    cout << mark(homework,test,examinstion);
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n , a , b  , c;
    cin >> a >> b >> c;
    a *= 0.2;
    b *= 0.3;
    c *= 0.5;
    n = a + b + c;
    cout << n;
    return 0;
}

A

泰裤辣！！！👍

#include <bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c,x;
    cin >> a >> b >> c;
    x = a * 0.2 + b * 0.3 + c * 0.5;
    cout << x;
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
double a, b, c;
int main()
{
    cin >> a >> b >> c;
    a *= 0.2; //20% = 0.2
    b *= 0.3; //30% = 0.3
    c *= 0.5; //50% = 0.5
    cout << a + b + c; //输出总和
    return 0;
}