In C++ please

Write a program that will read in grades, the number of grades should also be input by the user. The program will find the sum of those grades and pass it, along with the number of grades, to a function which has a "pass by reference" parameter that will contain the numeric average of those grades as processed by the function. The main function will then determine the letter grade of that average based on a 10-point scale. . 90-100 A 80-89 B 10-79 C . 60-69 D . 0-59 F DO NOT USE GLOBAL VARIABLES FOR THIS PROGRAM. Sample Run: Number of grades 3; Grades 90, 80, 50