2 or more digit numbers with delimiters in java

Question

I have this basic program that works pretty well when entering single digit numbers. But when calculating an expression with multiple digits, like 1337 - 456 + 32, the program doesn't move on...it acts likes I did nothing. It doesn't freeze or output an error message, it just stops.

here's the code:

import java.io.*;
import java.util.*;
public class Tester {
    public static void main(String args[]) {
        Scanner kb = new Scanner(System.in);
        System.out.print("Enter number: ");
        String s = kb.nextLine();
        Scanner sc = new Scanner(s);
        //Set delimiters to a plus sign surrounded by any amount of white space...or...
        // a minus sign surrounded by any amount of white space.
        sc.useDelimiter("\\s*");
        int sum = 0;
        int temp = 0;
        int intbefore = 0;
        
        if (sc.hasNext("\\-")) {
            sc.next();
            if (sc.hasNextInt()) {
                intbefore = sc.nextInt();
                int temper = intbefore * 2;
                intbefore = intbefore - temper; 
            }
        }
        if (sc.hasNextInt()) {
            intbefore = sc.nextInt(); //now its at the sign (intbefore = 5)
        }
        sum = intbefore;
        
        while (sc.hasNext()) {
            if(sc.hasNext("\\+")) { //does it have a plus sign?
                sc.next(); //if yes, move on (now at the number)
                System.out.println("got to the next();");
                
                if(sc.hasNextInt()) { //if there's a number
                    temp = sc.nextInt();
                    sum = sum + temp; //add it by the sum (0) and the sum of (5) and (4)
                    System.out.println("added " + sum);
                }
            }
            if(sc.hasNext("\\-")) {
                sc.next();
                System.out.println("got to the next();");
                
                if (sc.hasNextInt()) {
                    temp = sc.nextInt();
                    sum = sum - temp; //intbefore - temp == 11
                    System.out.println("intbefore: " + intbefore + "  temp: " + temp);
                    System.out.println("subtracted " + sum); // subtracted by 11
                }
            }
        }
        System.out.println("Sum is: " + sum);
    }
}

Help with why this happens and what to do to fix it? (I'm using netbeans if that helps)

Also, I'm assuming that the input has a space between each number Ex: 123 + -23 - 5

Answer 1

Try to change the dilimeter as "\\s+" in the first place or just use the default one

Answer 2

I tried to execute your code and this is what i found.

Suppose your input was 12+1.

Not sc.hasNextInt() will give you 1 which you are assigning to intbefore.

Next the while loop in your code is going to infinite loop cos sc.hasNext() will always be true (and returning 2 in this case ) and it doesn't match the two if conditions inside the while loop thus making your code run in infinite loop. Now go ahead and work on that. All the best.