/*
Phil Lane
10/10/17
Program Assignment 11
This program is entirely my own work.
*/

//Header files
#include <stdio.h>
#include <stdlib.h>

//Function prototype to get grade
void getGrade(int gradeNum, char** gradeStr);

//Main function
int main()
{
    char response;

    do
    {
        //Grade numeric value
        int gradeNum = 0;
        //Grade letter value
        char* gradeStr = (char*)calloc(3, sizeof(char)); //allocate three bytes

        //Repeat the scanf call until it's a valid input (for error checking)
        do
        {
            printf("Input a grade from 0 to 100:\n");
            scanf("%d", &gradeNum);
        } while (gradeNum < 0 || gradeNum > 100);

        //Call the getGrade function to assign value to gradeStr
        getGrade(gradeNum, &gradeStr);

        //Print the letter grade
        printf("You got a %s!\n", gradeStr);

        do
        {
            printf("Want to go again? (y/n):\n"); //query for y/n
            scanf(" %c", &response); //get response
            if (response > 'a') //if letter is lowercase
                response -= 32; //make it uppercase
        } while (response != 'Y' && response != 'N'); //for error checking, repeat until we get a valid response

    } while (response == 'Y'); //if yes, repeat the program
}

//takes the grade number and a pointer to a string that represents the letter grade
void getGrade(int gradeNum, char** gradeStr)
{
    //a 100 messes up the following switch statements so we manually handle this
    if (gradeNum == 100)
    {
        *gradeStr = "A+";
        return;
    }

    //First we check the grade. Divide by 10 and cast to int... that way we compare the first digit
    switch ((int)(gradeNum / 10))
    {
    case 9: //if grade is in the 90s
        (*gradeStr)[0] = 'A';
        break;
    case 8: //if grade is in the 80s
        (*gradeStr)[0] = 'B';
        break;
    case 7: //if grade is in the 70s
        (*gradeStr)[0] = 'C';
        break;
    case 6: //if grade is in the 60s
        (*gradeStr)[0] = 'D';
        break;
    default: //otherwise
        (*gradeStr)[0] = 'F';
        return; //return instead of break because there are no F+'s or F-'s
    }

    //now we handle the + or -. Mod 10 to get just the last digit
    switch (gradeNum % 10)
    {
    case 7: case 8: case 9: //if it's a X7, X8, or X9 then it's a +
        (*gradeStr)[1] = '+';
        break;
    case 0: case 1: case 2: case 3: //if it's a X0, X1, X2, or X3, then it's a -
        (*gradeStr)[1] = '-';
        break;
        //no default because we want it to be 0 to terminate the string
    }
}