Write a program to calculate the average GPA:

$1.$ First let the use enter the number of courses;

$2.$ Then let the user enter the grade for each course;

$3.$ Print the average GPA.

The formula for GPA: $4$ for grade $>=90,3$ for grade $>=80,2$ for grade $>=70,1$ for grade $>=60,0$ otherise

Here is a sample screen when running the program: