Grader.Service.cs

namespace Grader.Service
{
    public class GradeConverter
    {
        /// <summary>
        /// This function will take in a positive integer representing a grade percentage
        /// and return the letter grade corresponding to that percentage.
        /// </summary>
        public char GetLetterGrade(int grade) 
        {            
            if (grade >= 90)
            {
                return 'A';
            }
            // As per the requirements we will always include the lower bound number
            // in the middle cases
            if (grade < 90 && grade >= 80)
            {
                return 'B';
            }
            if (grade < 80 && grade >= 70)
            {
                return 'C';
            }
            if (grade < 70 && grade >= 60)
            {
                return 'D';
            }
            if (grade < 60)
            {
                return 'F';
            }

            // this should never happen, but if it does then we know something is wrong.
            throw new System.Exception("No letter grade found for that percentage");
        }
    }
}

Requirements.txt

We need a function that converts a percentage into a letter grade.
The mapping should be as follows:

 - 90 and above (including 90) should be given an A

 - 80 - 90 (including 80) should be given a B

 - 70 - 80 (including 70) should be given a C
 
 - 60 - 70 (including 60) should be given a D
 
 - Anything below (but NOT including 60) should be given an F