Write a C Sharp (C#) program that calculates a student's GPA. Remember, an A is worth 4 points, a B is worth 3 points, a C is worth 2 points, a D is worth 1 point, and an F is worth 0 points. For the purposes of this assignment, assume that all classes carry the same number of credit hours.

Use a sentinel-controlled loop to gather a variable number of letter grades. This should terminate the loop if the user enters an "X." This means that users should input as many grades as they like. When they are finished, they need to input an X, and at that point, the program will return the results.