2278. Percentage of Letter in String

Given a string s and a character letter, return the percentage of characters in s that equal letter rounded down to the nearest whole percent.

class Solution {
public:
    int percentageLetter(string s, char letter) {
        int count = 0;
        for(auto& ch : s)
            if(ch == letter) count++;
        double res = 100.0 * count / s.length();
        return floor(res);
    }
};