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Thread: Cannot Find Variable/Symbol Errors... why?

  1. #1
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    Default Cannot Find Variable/Symbol Errors... why?

    I keep getting errors from the compiler saying it can't find the symbols a,b and c in this class. Unless I'm blind, I think I clearly defined them in the first part of the code.
    public class Algebra {
      public void linearAlg() {
        System.out.println("Enter variables a b and c in ax+b=c");
        try {
          CalcInput user = new CalcInput();
          String userInput = user.getUserInput(" ");
          double a = Double.parseDouble(userInput);
          String userInput2 = user.getUserInput(" ");
          double b = Double.parseDouble(userInput2);
          String userInput3 = user.getUserInput(" ");
          double c = Double.parseDouble(userInput3);
        } catch(NumberFormatException e) {
          System.out.println("Your input was invalid.  Only numeric real entries are accepted.");
          System.out.println("Do not use operators.  Enter the a,b and c variables in ax+b=c");
          System.out.println("");
        } catch(NullPointerException e) {
          System.out.println("There must be an input!");
          System.out.println("");
        }
        if(b < 0) {
          AlgebraHelper helper = new AlgebraHelper();
          helper.setVars(b,c);
          double addNum = helper.addThis();
          helper.setVars(addNum,c);
          double divNum = helper.divThis();
          System.out.println(divNum);
        } else if(b == 0) {
          AlgebraHelper helper = new AlgebraHelper();
          helper.setVars(a,c);
          double divNum = helper.divThis();
          System.out.println(divNum);
        } else {
          AlgebraHelper helper = new AlgebraHelper();
          helper.setVars(b,c);
          double subNum = helper.subThis();
          helper.setVars(subNum,c);
          double divNum = helper.divThis();
          System.out.println(divNum);
        }
      }
    }

    Is it because the a,b,c variables are being used inside of a loop?

    If that is the case, how do I get the previously defined symbols to be recognized in the loop?


  2. #2
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    Default Re: Cannot Find Variable/Symbol Errors... why?

    Read this:

    Help with program

  3. #3
    mmm.. coffee JavaPF's Avatar
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    Default Re: Cannot Find Variable/Symbol Errors... why?

    Hello bgroenks96.

    This is a simple error.

    You get this because you are attempting to call these variables which are defined within the try/catch. They are unreachable.

    To demonstrate this, you can see how the error stops when you remove the try/catch blocks.

    public class Algebra {
    	public void linearAlg() {
     
    		System.out.println("Enter variables a b and c in ax+b=c");
     
    			CalcInput user = new CalcInput();
    			String userInput = user.getUserInput(" ");
    			double a = Double.parseDouble(userInput);
    			String userInput2 = user.getUserInput(" ");
    			double b = Double.parseDouble(userInput2);
    			String userInput3 = user.getUserInput(" ");
    			double c = Double.parseDouble(userInput3);
     
    		if (b < 0) {
    			AlgebraHelper helper = new AlgebraHelper();
    			helper.setVars(b, c);
    			double addNum = helper.addThis();
    			helper.setVars(addNum, c);
    			double divNum = helper.divThis();
    			System.out.println(divNum);
    		} else if (b == 0) {
    			AlgebraHelper helper = new AlgebraHelper();
    			helper.setVars(a, c);
    			double divNum = helper.divThis();
    			System.out.println(divNum);
    		} else {
    			AlgebraHelper helper = new AlgebraHelper();
    			helper.setVars(b, c);
    			double subNum = helper.subThis();
    			helper.setVars(subNum, c);
    			double divNum = helper.divThis();
    			System.out.println(divNum);
    		}
    	}
    }

    To fix, just place the if statements within the try/catch like so:

    public class Algebra {
      public void linearAlg() {
        System.out.println("Enter variables a b and c in ax+b=c");
        try {
          CalcInput user = new CalcInput();
          String userInput = user.getUserInput(" ");
          double a = Double.parseDouble(userInput);
          String userInput2 = user.getUserInput(" ");
          double b = Double.parseDouble(userInput2);
          String userInput3 = user.getUserInput(" ");
          double c = Double.parseDouble(userInput3);
     
     
          if(b < 0) {
              AlgebraHelper helper = new AlgebraHelper();
              helper.setVars(b,c);
              double addNum = helper.addThis();
              helper.setVars(addNum,c);
              double divNum = helper.divThis();
              System.out.println(divNum);
            } else if(b == 0) {
              AlgebraHelper helper = new AlgebraHelper();
              helper.setVars(a,c);
              double divNum = helper.divThis();
              System.out.println(divNum);
            } else {
              AlgebraHelper helper = new AlgebraHelper();
              helper.setVars(b,c);
              double subNum = helper.subThis();
              helper.setVars(subNum,c);
              double divNum = helper.divThis();
              System.out.println(divNum);
            }
     
     
        } catch(NumberFormatException e) {
          System.out.println("Your input was invalid.  Only numeric real entries are accepted.");
          System.out.println("Do not use operators.  Enter the a,b and c variables in ax+b=c");
          System.out.println("");
        } catch(NullPointerException e) {
          System.out.println("There must be an input!");
          System.out.println("");
        }
     
      }
    }
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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  4. The Following User Says Thank You to JavaPF For This Useful Post:

    bgroenks96 (June 8th, 2011)

  5. #4
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    Default Re: Cannot Find Variable/Symbol Errors... why?

    JavaPF,

    Thank you! Now I know... if variables are inside the Try/Catch they are unreachable. I will make the change.

    I designed it that way simply because I know it's generally better to have try and catch only in the part of the program that needs it. However, if it causes variables to become unreachable, it's probably better not to do that!

    Thank for your help. I was pretty confused on this one.

  6. #5
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    Default Re: Cannot Find Variable/Symbol Errors... why?

    All of which was explained in my explanation in the post I linked to. But I guess it was too hard for you to follow that link and read what I said. No thanks for me and no more help for you!

  7. #6
    mmm.. coffee JavaPF's Avatar
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    Default Re: Cannot Find Variable/Symbol Errors... why?

    Quote Originally Posted by Junky View Post
    All of which was explained in my explanation in the post I linked to. But I guess it was too hard for you to follow that link and read what I said. No thanks for me and no more help for you!
    Indeed all of this was in the link provided. I just felt like expanding on your answer.
    Your contributions are appreshiated as always Junky!
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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