C Programming Homework:

Create a one-dimension array to read 20 alphabetical letters (your program should be able to detect and print out an error message if a non-alphabetical letter is inputted). As each letter is entered, print it only if it has been entered before. Write a function that can sort the array after all 20 letters have been entered. Write another function that print out the most frequent letter and number of time it was entered. Prepare for the case where all 20 letters are different, or all are the same. Use the smallest possible variables and minimum array size to solve the