c++ programming. if you would please write some comments to explain how it was solved. thank you!

Write a program with at least six (6) functions by using while loop. The program should be able to count and display the number of student with grade A+ (90 - 100), grade A (80 - 89), grade B (70-79) and grade E (0 - 69). The program should also be able to display average of marks. The program should be able to check that the marks must be between 0 and 100. The first input is the number of students, for example 3. Then, the user must key in 3 marks. Finally, the program should be able to display the intended outputs. Input Validation: Display an error message if the user enters invalid inputs and ask the user to key in the new inputs by using loop or iteration