Thread: Variables not initialized?

I've just started learning Java and I'm currently writing a code for a homework project. This is the description:
Write an application that lets the user add, subtract, multiply, or divide two fractions. Use the rational class for your application.

This is what I have so far: (I added the last part in case someone typed capitals)

import java.util.*;
public class chap4pp7
{public static void main() { 
        Scanner scan = new Scanner(System.in); 
        Rational r1; 
        Rational r2; 
        Rational r3, r4, r5, r6; 
        System.out.println("First fraction's numerator: " );
        int a = scan.nextInt();
        System.out.println("First fraction's denominator: " );
        int b = scan.nextInt();
        System.out.println("Second fraction's numerator: ");
        int c = scan.nextInt();
        System.out.println("Second fraction's denominator: ");
        int d = scan.nextInt(); 
 
        r1 = new Rational(a,b);
        r2 = new Rational(c,d);
 
        int add, subtract, multiply, divide; 
        System.out.println("Please type in the desired function (no caps)-- add, subtract, multiply,"
            + "or divide: ");
        int e = scan.nextInt();
        int Add, Subtract, Multiply, Divide;
 
        if (e == add){
            r3 = r1.add(r2);  
            System.out.println("Your total is: " +r3);
        }
            else 
            if (e == subtract){ 
                r4 = r1.subtract(r2);
            System.out.println("Your total is: " +r4);
        }
            else 
            if (e == multiply){
                r5 = r1.multiply(r2);
            System.out.println("Your total is: " +r5);
        }
            else 
            if (e == divide){
                r6 = r1.divide(r2);
            System.out.println("Your total is: " +r6); 
        }
 
            //the next part is just in case the user types with capitals. 
            //i am aware this part isn't necessary it's just for me
            //I did them each separately. 
            else 
            if (e == Add){
            System.out.println("Please type in lowercase.");
        }
            else
            if (e ==Subtract){
            System.out.println("Please type in lowercase."); 
        }
            else
            if (e == Multiply){
            System.out.println("Please type in lowercase.");
        }
            else
            if (e == Divide){
            System.out.println("Please type in lowercase.");
 
        } 
}
}

My issue was with the beginning of all of the if statements. When I tried to compile, I got an error message that said "variable add might not have been initialized". The problem was in the line if(e==add). I assume it is the same issue with all of the following variables as well. What can I do to fix this? Also, why is the program uncertain? MIGHT not have been initialized?
Anyway thanks in advance for your help! I realize this isn't the slickest code on the block but if you see any other errors feel free to let me know!

--- Update ---

OH GOD i just realized i posted this in the wrong sub forum i think.
FORGIVE ME I DIDN'T SEE IT BEFORE

set them equal to 0? where I had them established before?

IT WORKED! thanks for your help do you see any other issues or anything with my code?

Have you tested your code beside compiling it? Just a few issues that you may have fixed already.

For example in this code block:

        // What are the ints for? The are declared but initialization has not happened
        int add, subtract, multiply, divide;
 
        // In this line of code you ask the user to type in desired function (Strings) from the sounds of it but your program expects int. When the user types in add and it expects an int your application will complain and crash. You could rephrase and ask to type the number of function desired sort of a menu or you could also ask for a string but it will be slightly more involved. Not difficult just a little bit of learning.
        System.out.println("Please type in the desired function (no caps)-- add, subtract, multiply,"
            + "or divide: ");
        int e = scan.nextInt();
 
        // Same as first set of ints created. They are declared but not initialized.  Ints can only take whole numbers (1,2,3,4,5...etc)
        int Add, Subtract, Multiply, Divide;

Another thing is how are you gonna let your program know what function to do?

if (e == add){
   // code
}
else if (e == subtract){
  // code
}
//... etc

What is the difference between add and subtract? In the upper portion of your program you assign both of them the same value. How will the application know the difference of an int that is 0 vs an int that is 0? In an if-else statement it will run the first condition that is true. So if they are both set to the same value it will always run add portion.

Keep in mind when Declaring variables it is always
Datatype variableName = some value;

I think you are confusing how to use variables and are mistakenly using the name as a way of differentiating ("add" or "Add") which are actually Strings.