CODEWITHSUNDEEP
java
Nawa
Nawa

Reputation: 45

why the value inside 'if statement' in java cannot be accessed outside of 'if statement'?

following code is giving error message as 'Exception in thread "main" java.lang.Error: Unresolved compilation problem: The local variable answer may not have been initialized'.

package firstproject;
import java.util.Scanner;

public class calculator {
    public static void main(String args[]){

        double firstno, secondno, answer;
        int choice;
        Scanner add = new Scanner(System.in);

        System.out.println("What r u trying to do??");
        System.out.println("1 - add");
        System.out.println("2 - substract");
        System.out.println("3 - multiplication");
        System.out.println("4 - division");

        choice = add.nextInt();

        System.out.print("Enter your 1st number: ");
        firstno = add.nextDouble();

        System.out.print("Enter another number: ");
        secondno = add.nextDouble();

        if(choice == 1){
            answer = firstno + secondno;
        }
        if(choice == 2){
            answer = firstno - secondno;
        }
        if(choice == 3){
            answer = firstno * secondno;
        }
        if(choice == 4){
            answer = firstno / secondno;
        }

        System.out.println("answer: " + answer);
    }
}

so, i did something like this

package firstproject;
import java.util.Scanner;

public class calculator {
    public static void main(String args[]){

        double firstno, secondno, answer;
        int choice;
        Scanner add = new Scanner(System.in);

        System.out.println("What r u trying to do??");
        System.out.println("1 - add");
        System.out.println("2 - substract");
        System.out.println("3 - multiplication");
        System.out.println("4 - division");

        choice = add.nextInt();

        System.out.print("Enter your 1st number: ");
        firstno = add.nextDouble();

        System.out.print("Enter another number: ");
        secondno = add.nextDouble();

        if(choice == 1){
            answer = firstno + secondno;
            System.out.println("Answer: " + answer);
        }
        if(choice == 2){
            answer = firstno - secondno;
            System.out.println("Answer: " + answer);
        }
        if(choice == 3){
            answer = firstno * secondno;
            System.out.println("Answer: " + answer);
        }
        if(choice == 4){
            answer = firstno / secondno;
            System.out.println("Answer: " + answer);
        }
    }
}

it worked. but i want to know why my first code didn't work.

Upvotes: 1

Views: 3958

Answers (6)

Gary D.Guo
Gary D.Guo

Reputation: 9

  1. The var "answer" may not be inited if "choice" does not belong to "1,2,3,4". So when you try to print it at the very end, this exception may happen.

  2. The second one actually has the same problem, the only reason that makes it work is you moved the print line up to each blocks. So when "choice" does not belong to "1,2,3,4", the code needs to do nothing. And it will be considered as "No problem".

  3. For the fix, all of them above :)

Upvotes: 0

Andrew
Andrew

Reputation: 1292

"The local variable answer may not have been initialized" is accurate. If the user types in "5", then answer doesn't get set to any value. Try defining answer as "answer = 0.0".

Upvotes: 0

Khurram Sharif
Khurram Sharif

Reputation: 504

Initialize the answer with some values like answer=-1 before printing, because how we can print a null reference

once any variable initialized it can be use in body of conditional statements

suppose You don't enter valid choice , what would be the value in answer , while answer is just act like a null reference

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1502006

Local variables in Java can't be read unless they're definitely assigned - in other words, if the compiler can prove that every way that you can get to the expression that's trying to read the variable will have gone through an assignment to that variable.

In your case, if choice isn't 1, 2, 3 or 4 you won't have gone through an assignment.

Ways of fixing this:

  • Specify an initial value as part of the variable declaration

  • Change your if series to an if/else series with a plain else at the end, which either terminates the method or assigns a value. For example:

    if (choice == 1) {
    answer = firstno + secondno;
} else if (choice == 2) {
    answer = firstno - secondno;
} else  if (choice == 3) {
    answer = firstno * secondno;
} else if(choice == 4) {
    answer = firstno / secondno;
} else {
    System.out.println("Invalid choice");
    return; // Or assign a value to answer
}
  • Use a switch statement instead of your if statements, and provide a default case which either assigns to answer or returns

Upvotes: 3

jp-jee
jp-jee

Reputation: 1523

You can access it, but if none of your conditions was true, answer will not be initialized when you are trying to print it.

Initialize it with double answer = 0.

Upvotes: 5

null
null

Reputation: 5255

if all the conditions in all ifs are false, the variable answer will indeed not be initialized.

Say choice is 42245234, what value does answer have in this line?

System.out.println("answer: " + answer);

Upvotes: 0

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