: GPA ConverterIn the CSC$262$ Course Outline, there is a Grade Table that shows the conversion from course grades in points to letter grades $($A$,$ A$-,$ B$+,$ etc.$)$ and from letter grades to GPA number grade. Your instructor is responsible for assigning the course grades in points and converting them to letter grades. Please write a program that converts a letter grade into a GPA grade. If the user enters anything other than a valid letter grade, please display a descriptive error message before exiting the program.