这才是本题真正的答案：

#include <bits/stdc++.h>
using namespace std;
int main()
{
    cout << "AAAAAAAAA" << endl;
    cout << "BBBBBBBBB" << endl;
    cout << "CCCCCCCCC" << endl;
    cout << "DDDDDDDDD" << endl;
    cout << "EEEEEEEEE" << endl;
    cout << "FFFFFFFFF" << endl;
    cout << "GGGGGGGGG" << endl;
    cout << "HHHHHHHHH" << endl;
    cout << "IIIIIIIII" << endl;
    return 0;
}

我来发我的正解啦！！！

#include <bits/stdc++.h>
using namespace std;
int main()
{
    char c = 'A';
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= n; j++)
            cout << c;
        cout << endl;
        c++;
    }
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
    	for(int j=0;j<n;j++){
        	cout<<(char)('A'+i);
    	}
        cout<<endl;
    }
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        char x;
        for(int j=0;j<n;j++)
        {
            x='A'+i;
            cout<<x;
        }
        cout<<endl;
    }
    return 0;
}