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Thread: Why won't this code loop?

  1. #1
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    Default Why won't this code loop?

    Hello everyone, I'm brand new to java and also to this forum. Hoping to get some help and maybe help others when I get better at this.

    Ok, so I tried to make a loop, if you enter "y" the code is supposed to loop, otherwise the program should terminate, but for some reason it won't loop, and I can't figure out what I'm doing wrong...

    import java.util.Scanner;
     
    public class scanner {
    	public static void main (String args[]){
     
    		Scanner scn = new Scanner(System.in);
    		Scanner go = new Scanner(System.in);
     
    		int fnum, snum, answer;
    		String yn = "y";
     
    		while(yn == "y"){	// this is there my loop starts
     
    			System.out.print("enter first number: ");
    			fnum = scn.nextInt();
    			System.out.print("enter second number: ");
    			snum = scn.nextInt();
    			answer = fnum - snum;
    			System.out.println(fnum + " - " + snum + " = " + answer);
     
    			System.out.print("go again (y/n)? ");
    			yn = go.nextLine();
    			System.out.print(yn);	// just so make sure yn="y"
    		}	
    	}
    }
    Last edited by Joniverse; March 29th, 2012 at 03:53 AM.


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Why won't this code loop?

    Use the equals method to compare Strings, not the == operator.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Why won't this code loop?

    If i do that, i get a "Type mismatch: cannot convert from Strings to boolean"...

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    Super Moderator Norm's Avatar
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    Default Re: Why won't this code loop?

    Please post the code that created the error message.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Why won't this code loop?

    It is this one, here without the ==.

    The error message reads:
    Exception in thread "main" java.lang.Error: Unresolved compilation problem:
    Type mismatch: cannot convert from String to boolean

    at scanner.main(scanner.java:12)

    import java.util.Scanner;
     
    public class scanner {
    	public static void main (String args[]){
     
    		Scanner scn = new Scanner(System.in);
    		Scanner go = new Scanner(System.in);
     
    		int fnum, snum, answer;
    		String yn = "y";
     
    		while(yn = "y"){	// this is there my loop starts
     
    			System.out.print("enter first number: ");
    			fnum = scn.nextInt();
    			System.out.print("enter second number: ");
    			snum = scn.nextInt();
    			answer = fnum - snum;
    			System.out.println(fnum + " - " + snum + " = " + answer);
     
    			System.out.print("go again (y/n)? ");
    			yn = go.nextLine();
    			System.out.print(yn);	// just so make sure yn="y"
    		}	
    	}
    }
    Last edited by Joniverse; March 29th, 2012 at 10:10 AM.

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: Why won't this code loop?

    while(yn = "y"){	// this is there my loop starts
    The while statement requires a boolean value inside of the ().
    Your code has an assignment statement inside of the ()s that evaluates to a String.
    cannot convert from String to boolean
    The compiler is complaining that there is no way to convert the String to the required boolean

    Where are you using the equals() method that I recommended?
    If you don't understand my answer, don't ignore it, ask a question.

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