#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int x = n, c = n, num = 0, sum = 0;
    while (x > 0)
    {
        if (x % 10 == 5)
        {
            sum++;
            break;
        }
        x /= 10;
    }
    if (sum == 1)
    {
        while (c > 0)
        {
            num += c % 10;
            c /= 10;
        }
        cout << num;
    }
    else
    {
        cout << n;
    }
    return 0;
}

最简代码，已AC放心食用

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin >> n;
    if(n % 10 == 5 || n / 10 % 10 == 5 || n / 100 % 10 == 5 || n / 1000 % 10 == 5 || n / 10000 == 5)
    {
        cout << n % 10  + n / 10 % 10  + n / 100 % 10  + n / 1000 % 10 + n / 10000;
    }
    else
    {
        cout << n;
    }
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int x;
    cin>>x;
    if (x/10000==5||x/1000%10==5||x/100%10==5||x/10%10==5||x%10==5)
        cout<<x/10000+x/1000%10+x/100%10+x/10%10+x%10;
    else
        cout<<x;
    return 0;
}