Add and Subtract

Question

I feel like I've tried everything, searched everything I know to search, and I've been working on this for about 6 classes now.

I'm trying to make a program that accepts a string input like "6 + 6 -3+ 2", and can add/subtract everything to output the correct answer. I got it to work with either addition or subtraction at one time (can't do anything like "6 + 6 - 3") and there also always have to be a space between any digit. It also can't add multi-digit numbers, but I'll worry about that once it can correctly add/subtract in the first place.

So I don't think I'm understand how Scanner and delimiters work, (since that's what the chapter is on) but I can't seem to find anything online that's helped me understand what I'm doing wrong.

This is what I have so far:

package addEmUp; import java.util.*; public class TesterShell { public static void main(String[] args){ Scanner kbIn = new Scanner(System.in); System.out.print("Enter some addition/subtraction problem: "); String s = kbIn.nextLine(); Scanner numChecker = new Scanner(s); Scanner valueChecker = new Scanner(s); numChecker.useDelimiter("\\s*\\+\\s*|\\s*\\-\\s*"); int sum = 0; while(numChecker.hasNext()){ if(valueChecker.next().equals("-")){ sum = sum - numChecker.nextInt(); } else{ sum = sum + numChecker.nextInt(); } System.out.println(sum); //Just for checking what's going on, will remove in the end } System.out.println("Sum = " + sum); } }

Based on the other questions I've found on StackOverflow, a better way to do this would be to use index, but the Chapter I'm in set me up with a shell program using strings and scanner.

What am I missing here? What did I misunderstand/not understand at all?

See this post: stackoverflow.com/questions/4589951/… or this one: stackoverflow.com/questions/1432245/… — Jorge Campos
– Jorge Campos, Commented Dec 10, 2013 at 19:02

Konstantin · Accepted Answer · 2013-12-10 19:17:16Z

2

For plain addition/subtraction you can do something simple like

String[] nums = s.replaceAll(" ", "").replaceAll("\\+", " ") .replaceAll("-", " -").split(" "); int res = 0; for (String n : nums) { if (!n.isEmpty()) res += Integer.parseInt(n); }

answered Dec 10, 2013 at 19:17

Konstantin

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1 Comment

ananaso Over a year ago

Well, I was looking for a way to use delimiter since that's what my tutorial/book was looking for, but w/e. I think I'll switch to the official Java Tutorials now, since they seem much more clear than my current tutorial (who would'a thunk?). Also, some stuff I didn't know in there (but now I do, since I looked it up to understand this answer), like arrays. Thanks!

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