C program only, no C++ or C#

Write a program that will allow the user to enter several sentences, and then produce a frequency analysis for each letter. The program should state which letter occurred the most often. Uppercase letters and lowercase letters should be treated the same. Ignore any punctuation symbols that were entered.

Sample output: Letter Frequency: a - 10 b - 2 c - 4 d - 11 The letter 'e' was the most frequently used letter.