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Thread: Error with String range print -1.

  1. #1
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    Default Error with String range print -1.

    Scanner input = new Scanner(System.in);

    int x = 0;

    System.out.println(" Enter a math operation: ");
    String expr = input.next();

    int pos = expr.indexOf("+");

    if ( pos >= 0) {
    int op1 = Integer.parseInt(expr.substring(0, pos));
    int op2 = Integer.parseInt(expr.substring( pos - x , expr.length()));
    System.out.println( op1 + op2);
    } else
    if (pos == expr.indexOf("-")) {
    int op1 = Integer.parseInt(expr.substring(0, pos));
    int op2 = Integer.parseInt(expr.substring( pos - x , expr.length()));
    System.out.println( op1 - op2);
    } else
    if (pos == expr.indexOf("/")) {
    int op1 = Integer.parseInt(expr.substring(0, pos));
    int op2 = Integer.parseInt(expr.substring( pos - x , expr.length()));
    System.out.println( op1 / op2);
    } else
    if (pos == expr.indexOf("%")) {
    int op1 = Integer.parseInt(expr.substring(0, pos));
    int op2 = Integer.parseInt(expr.substring( pos - x , expr.length()));
    System.out.println( op1 % op2);
    }
    else {
    System.out.println(" Invalid operation ");
    }
    }
    }
    ALthough this gets compiled, the program automatically says

    an ex out of range: -1
    at java.lang.String.substring(String.java:1937)
    at MathFun.main(MathFun.java:21)
    Is there something wrong with the loop? I just want to make a simple loop that lets the user enter a string 2+2 and let the loop read that out as a string and print the result. Thank You!


  2. #2
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    Default Re: Error with String range print -1.

    int pos = expr.indexOf("+");
    What happens when the user enters an expression that is not addition? The indexOf method returns -1 when it cannot find the target char.
    Improving the world one idiot at a time!

  3. #3
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    Default Re: Error with String range print -1.

    How would I make it so it finds it instead? In other words, how would I initialize it? I'm sorry if this is confusing, but I don't understand this much.

  4. #4
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    Default Re: Error with String range print -1.

    You need to rework your if statements. All the other (- / %) are kinda on the right track but you are comparing each value returned from indexOf to pos. Get rid of pos and compare the returned value to .....

    I leave that as exercise for you to think about. Hint: how does the first if statement work?
    Improving the world one idiot at a time!

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