Programming Challenge 10.9 - Most Frequent Character

/* Most Frequent Character - This program contains a function that accepts
    a string object as its argument. The function returns the character that
    appears most frequently in the string. */

#include "Utility.h"

/* Finds the most frequently occuring character in the string,
    stores the frequency in a reference variable, returns the
    most frequently occuring character */
char mostFreq(string, unsigned int &);

int main()
{
    unsigned int frequency = 0;
    char             mostFreqChar = ' ';    
    string         sentence = " ";
  
    cout << "\n\tMost Frequent Character\n\n"
          << "\tEnter a sentence, and I will show you, what the most\n"
          << "\tfrequently occuring character is.\n\n"
          << "\tPlease enter your sentence: ";
    getline(cin, sentence);

    mostFreqChar = mostFreq(sentence, frequency);

    cout << "\n\tThe most frequent character is "
          << '\'' << mostFreqChar << '\'' << ", appearing "
          << frequency << " times in your sentence.";

   pauseSystem();
   return 0;
}

/* **********************************************************
    Definition: mostFreq

    This function accepts a string class object as argument.
    It determines the most frequently appearing character in
    the string and returns it. The frequency in which this
    character appears is stored in a reference variable.
   ********************************************************** */

char mostFreq(string sentence, unsigned int &frequency)
{
    unsigned int index = 0,
                     startScan = 0,
                     charCount = 0;
    char             mostFreqChar = ' ';

    for (startScan = index + 1; startScan < sentence.size(); startScan++)
    {
        charCount = 0;

        for (index = 0; index < sentence.size(); index++)
        {
            if (isalpha(sentence[index]) && isalpha(sentence[startScan]))
            {
                if (tolower(sentence[startScan]) == tolower(sentence[index]))
                {
                    charCount++;
                }

                if (charCount > frequency)
                {
                    frequency = charCount;
                    mostFreqChar = (tolower(sentence[index]));
                }
            }
        }
    }

    return mostFreqChar;
}

Example Output: