Project 2-2: Grade Converter
Create an application that converts number grades to letter grades.

Console
Welcome to the Letter Grade Converter

Enter numerical grade: 90

Letter grade: A

Continue? (y/n): y

Enter numerical grade: 88

Letter grade: A

Continue? (y/n): y

Enter numerical grade: 80

Letter grade: B

Continue? (y/n): y

Enter numerical grade: 67

Letter grade: C

Continue? (y/n): y

Enter numerical grade: 59

Letter grade: F

Continue? (y/n): n

Specifications
The grading criteria is as follows:

A  88-100
B  80-87
C  67-79
D  60-67
F  <60

Assume that the user will enter valid integers between 1 and 100 for the grades.

The application should only continue if the user enters ‘y’ or ‘Y’ in response.