Why does this code not end?

Question

class Operation {
double add(double a, double b){
    double c;
    c = a+b;
    return c;
}
double sub(double a, double b){

    double c;
    c = a-b;
    return c;
}
double mul(double a, double b){
    double c;
    c = a*b;
    return c;
}
double div(double a, double b){
    double c;
    c = a/b;
    return c;
}
}

class Selection{    
static double x,y;
void sel(int a){
    Operation op = new Operation();
    Scanner sc = new Scanner(System.in);
    char b;
    if(a==1)
        b='+';
    else if(a==2)
        b='-';
    else if(a==3)
        b='*';
    else
        b='/';
    System.out.println(">>You have selected "+b+" operator");
    System.out.println(">>Please enter the first operand.");
    x = sc.nextDouble();
    System.out.println(">>Please enter the second operand.");
    y = sc.nextDouble();
    }
double x(){
    return x;
}
double y(){
    return y;
}
}


public class Calculator {
static int select;

public static void main(String [] args){
    Operation op = new Operation();
    Selection se = new Selection();
    Scanner sc = new Scanner(System.in);
    boolean run = true;


    while(run){
        System.out.printf(">>Select Operator\n>>1: +  2: -  3: *  4: /\n");
        select = sc.nextInt();

        if(select == 1){
            se.sel(1);
            double a = se.x();
            double b = se.y();
            double result = op.add(a, b);
            System.out.println(">>The result of "+a+" + "+b+" is "+result);

        }else if (select ==2){
            se.sel(2);
            double a = se.x();
            double b = se.y();
            double result = op.sub(a,b);
            System.out.println(">>The result of "+a+" - "+b+" is "+result);

        }else if (select ==3){
            se.sel(3);
            double a = se.x();
            double b = se.y();
            double result = op.mul(a,b);
            System.out.println(">>The result of "+a+" * "+b+" is "+result);

        }else if(select == 4){
            se.sel(4);
            double a = se.x();
            double b = se.y();
            double result = op.div(a,b);
            System.out.println(">>The result of "+a+" / "+b+" is "+result);

        }else {
            System.out.println(">>Your number is not available, please try again!");
            System.out.println();
            System.out.println();
            continue;
        }       


        System.out.println(">>Do you want to exit the program(y/n)?");
        String startOver = sc.nextLine();

        if(startOver.equals("y")){
            run = false;
            System.out.println(">>Thank you for using my program!");
        }else{
            continue;
        }
    }
}

}

So this is my calculation program for a high school homework. It works fine until, asking for quitting the program or keep continuing the code. Even if I want to quit the program, it restarts after showing the results. I think there's something wrong at the end of the code. Can somebody help?

Did you take a look at http://stackoverflow.com/a/5032408/875832 ? It looks like it's possible that it's always hitting the `else`, because there's a remaining newline from the previous input. I recommend you examine the contents of `startOver`. — Moshe, Oct 15 '13 at 13:27
Try debugging exactly what `startOver` gets when the user enters "y". I would wager that it contains "y" plus a newline character, which causes the `.equals("y")` check to fail. — jbabey, Oct 15 '13 at 13:27
@jbabey it was confusing as hell, but i finally figured out the problem. I changed 'sc.nextLine();' to 'sc.next();' and it works like magic. Like you said, i think that "Line" added a newline character. Thanks for the help! :D — Muon, Oct 15 '13 at 13:33

score 4 · Accepted Answer · answered Oct 15 '13 at 13:32

4

The problem is here:

String startOver = sc.nextLine();

When you read in the operand numbers with nextDouble(), the method leaves rest of the line in the parser/buffer.

So when you call nextLine() you are still reading the rest of the previous line. This will cause your startOver string to be empty and the if condition doesn't work as well.

I suggest you to use scan.next() instead of scan.nextLine()

answered Oct 15 '13 at 13:32

Cirou

1,360
11
18

Yeah, i changed it and it worked. I've got to study more about the differences! thanks! – Muon Oct 15 '13 at 13:37

Why does this code not end?

1 Answers1