Write in c++ as simple as possible.

3. Write a program that computes the average test score over an unspecified number of tests as follows: (1) Ask the user to enter numeric grades; (2) as long as there are more grades, add them to the total; (3) use a counter variable to track the number of grades entered by the user; (4) stop when the user enters a negative score; (5) output the average grade for the class. Enter a numeric grade: > 78 Enter a numeric grade: > 89 Enter a numeric grade: > 77 Enter a numeric grade: > 90 Enter a numeric grade: > 97 Enter a numeric grade: > 92 Enter a numeric grade: > -1 The average grade is 87.1667