Please use C++ code suitable for an intro to programming class. Use an array and map the letter read to an index in the answer. Thanks!

Write a program to calculate the frequency of occurrence of each letter in a given text file. Your program should not distinguish between lower case and upper case letters. The text may contain characters other than alphabets. You can ignore the non-alphabetic characters. Your output should display for each letter the appropriate times it occurred in the file. A sample output is shown beloW. Letter 'a' occurred 20 times Letter 'b' occurred 25 times Letter 'z' occurred 10 times The name of the text file should be given as an input to the program