letter grade to GPA program

Question

Beginner at Java here. So I'm stuck as to how I would go about making it so if the user input is "A+" I will get 4.0 and no higher? Similarly for "F", I want to make it so that F,F-,F+ all result in 0.0 gpa. I figured either I was going to put special parameters for letter grades A and F or just code a "limit" or a "cap" so to speak on the GPA. What I mean is making it so my double 'gpa' can only be values 0-4.0. Either method that you think works best is fine, I'm just so unfamiliar with the syntax and the vocabulary of Java that I don't know where to even begin.

Here's my code:

import java.util.*;
public class HomeworkCalculator {
    public static void main(String[] args) {
        Scanner in = new Scanner(System. in );
        String grade, letter1, letter2;
        System.out.print("Enter a letter grade: ");
        grade = in .nextLine();
        letter1 = grade.substring(0, 1);
        letter2 = grade.substring(1, 2);

        double gpa = 0;

        if (letter1.equals("A")) {
            gpa = 3.9;
        } else if (letter1.equals("B")) {
            gpa = 3.0;
        } else if (letter1.equals("C")) {
            gpa = 2.1;
        } else if (letter1.equals("D")) {
            gpa = 1.2;
        } else if (letter1.equals("F")) {
            gpa = 0;
        }

        if (letter2.equals("+")) {
            System.out.println(gpa + 0.3);
        } else if (letter2.equals("-")) {
            System.out.println(gpa - 0.3);
        }


    }
}

I tried individually coding the user input 'A+' to be only equal to 4.0 at the end of the program but then the output just gives me 4.0 and then 4.2 after that when I only want 1 value. I then tried adding a break or a return to see if I could make it so that IF the input was 'A+' it would automatically just end the code right then and there -- hopefully stopping any additional outputs from happening, but that didn't happen.

Any suggestions?

Answer 1

Naive solution here:

package testgrade;

import java.util.*;

public class Tg {

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String grade;
    System.out.print("Enter a letter grade: ");
    grade = in.nextLine();
    double gpa = 0.0;
    boolean bad_entry = false;
    int entered_grade_len = grade.length();
    // Verify entered content
    if (entered_grade_len <= 2 && entered_grade_len > 0) {
        if((grade.substring(0).toUpperCase() == "A") ||
           (grade.substring(0).toUpperCase() == "B") ||
           (grade.substring(0).toUpperCase() == "C") ||
           (grade.substring(0).toUpperCase() == "D") ||
           (grade.substring(0).toUpperCase() == "F"))
        {
            switch(entered_grade_len)
            {
            case 2:
                if((grade.substring(1) == "+") ||
                   (grade.substring(0).toUpperCase() == "-"))
                break;
            default:
                bad_entry = true;
                break;
            }

        }
    }
    if(bad_entry)
    {
        System.out.println("Usage: Enter grades in the normal spectrum from A(+/-) to F");
        System.out.println("eg: A+, B-, D+, C, F...");
        return;
    }
    String lettergrade = grade.substring(0,1).toString().toUpperCase();
    switch (lettergrade) {
    case "A":
        gpa = 4.0;
        break;
    case "B":
        gpa = 3.0;
        break;
    case "C":
        gpa = 2.0;
        break;
    case "D":
        gpa = 1.0;
        break;
    case "F":
        gpa = 0.0;
        break;
    default:
        break;
    }
    if (grade.length() > 1) {
        lettergrade = grade.substring(1, 2);
        switch (lettergrade) {
        case "+":
            if (gpa <= 3 && gpa >= 1.0)
                gpa += 0.3;
            break;
        case "-":
            if (gpa <= 4 && gpa >= 1.0)
                gpa -= 0.3;
            break;
        default:
            break;
        }
    }
    System.out.println(gpa);
    in.close();
}
}

This could be improved a ton with some regular expressions for the comparisons, but for quick and dirty it works. (A = 3.9? bah...but you could do as above, if gpa = 4 and grade.length() = 1) gpa -= 0.1)

Answer 2

Another possibility is that at the end of the entire section of code, you could add:

if (gpa > 4) gpa = 4;
if (gpa < 0) gpa = 0;
if (letter1.equals("F") && letter2.equals("+")) gpa = 0;

Answer 3

if (letter1.equals("A") && letter2.equals("+")) gpa = 4.0;
else if(letter1.equals("A"))
{gpa = 3.9;}
else if(letter1.equals("B")) 
{gpa = 3.0;}
else if(letter1.equals("C"))
{gpa = 2.1;}
else if(letter1.equals("D"))
{gpa = 1.2;}
else if(letter1.equals("F"))
{gpa = 0;}

if (!letter1.equals("F")) {
    if(letter2.equals("+") && !letter1.equals("A")) gpa += 0.3;
    else if(letter2.equals("-")) gpa -= 0.3;
}