Write a program that, given the name of a text file, reads that file and counts the number

of occurrences of each alphabetic letter in the file. Your program should print out the

occurrences result on the screen and ask the user to enter a file name to store the result.

Your program should use a vector of length $26$ to count the occurrences of the $26$

alphabet letters, and treat upper and lower$-$case instances of a letter as the same letter.

Hint:

$1.$ Use vector occurrences$(26)$;

$2.$ Use tolower$($letter$)$ function if the letter is uppercase $($slide $24$ of the lecture note

$$using classes$)$;

$3.$ Use letter $$a$$ as the index for the vector occurrences, i$.$e$.,$ occurrences $[$letter$-$a$]++.$

Therefore, occurrences$[0]$ expresses the occurrences of $$a$,$ occurrences$[1]$b$,...$

Example: In a file that said $$Hello World$,$ the vector occurrence would look like:

$[0,0,01,1,0,0,1,0,0,0,3,0,0,2,0,0,1,0,0,0,0,1,0,0,0$