What exactly does ++array[s.charAt(i) - 'A'] do?

Question

for (int i = 0; i < s.length(); ++i) 
    {
        if (s.charAt(i) >= \'A\' && s.charAt(i) <= \'Z\') 
        {
            ++array[s.charAt(i) - \         


        

Answer 1

++array[s.charAt(i) - 'A'];

count frequency of each character in given string s and store the frequency of each character at a particular index in the array.