I absolutely don't understand why you have so long answers :)
#include <iostream>
#include <string>
using namespace std;
int main() {
    string s; int counts, MaxCounts = 0; char MaxSymb;
    cin >> s;
    for (int i = 'A'; i <= 'z'; i++) {
        counts =count(s.begin(), s.end(), i);
        if (counts > MaxCounts) {
            MaxCounts = counts;
            MaxSymb = i;
        }
    }
    cout << MaxSymb;
}