CODEWITHSUNDEEP
javaexceptionstackqueuetry-catch
user3094226
user3094226

Reputation:

Stack Pop loop does not pop all elements

I am practicing Try-Catch, Exception Handling, and Stacks and Queues, so although the code may be impractical, it is useful for my practice.

public class Practice {
public static void main(String args[]){
    Stack<String> sStack = new Stack<String>();
    Queue<String> sQueue = new LinkedList<String>();
    Scanner input = new Scanner(System.in);
    String inString = " ";

    boolean done = false;
    do{
        try{
            while(!inString.equals("")){
                System.out.println("Enter a string: ");
                inString = input.nextLine().toString();
                addS(sStack,inString);
            }
            done = true;
        }catch(Exception e){}
        sStack.pop();
        for(int i = 0; i<sStack.size()+1;i++){
            remS(sStack);
        }

    }while(done == false);
}

The code is intended to loop through and populate an empty stack based on user input, and then loop through the stack and remove each element while giving a prompt. The first set I input is:

[art, bat, cat, dock, eye, father]

the second set is:

[art, bat, cat, dock, eye, father, kid]

I noticed that no matter how many elements I input it will only remove up to 4 elements. I would like your help in figuring out why. I tried playing around with the loop's bounds as you can see, but to no avail. No matter where I start or bound, it will always end up popping only 4 elements max.

The addS and remS functions I provide below

public static void addS(Stack t, String s){
    t.push(s);
    System.out.printf("%s was added to the stack %s", s, t);
    System.out.println();
}

public static void remS(Stack t){

    System.out.printf("\n%s has been popped.",t);
    t.pop();
    System.out.printf("The current elements are now: ");
    System.out.print(t);
    System.out.printf("The next element to be popped is %s", t.peek());
}

Upvotes: 0

Views: 10472

Answers (3)

java graduates
java graduates

Reputation: 101

use int i=1 intead of i=0. for example(int i=1;i<=n;i++).

import java.io.*;
import java.util.*;

public class Rev
{
public static void main(String args[]) throws IOException
{
Stack<String> v=new Stack<String>();
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
int n=Integer.parseInt(br.readLine());
 String[] arr=new String[n];
//String str=br.readLine();
for(int i=0;i<n;i++)
{
arr[i]=br.readLine();
 }
 System.out.println("entered data is");
for(int i=0;i<n;i++)
{

System.out.println(arr[i]);
 }
 for(int i=0;i<n;i++)
 {
 v.push(arr[i]);
}
 System.out.println("getting the element");
System.out.println(v.get(1));
v.set(1,"15");
System.out.println(v.get(1));
System.out.println("reversed String is");
for(int i=1;i<=n;i++)
{
System.out.println(v.pop());

  }

 } 
  }

Upvotes: 0

Eric Lippert
Eric Lippert

Reputation: 660397

This is a frequently asked question. This is a good opportunity for you to first, learn how to use your debugger, and second, learn how to think about programming problems logically.

    for(int i = 0; i<sStack.size()+1;i++){
        remS(sStack);
    }

This always removes half the items in the stack. Work out why by emulating the operation of the loop on paper and you will quickly see why.

Example of what I mean. Write down: 

stack contains A, B, C, D
i is 0
test loop condition: 0 is smaller than 4 + 1, so we enter the loop.
remove item from stack.
stack contains B, C, D
size is 3
execute loop increment: i is now 1
test loop condition: 1 is smaller than 3 + 1, so we enter the loop...

Finish it off.

OK, now that you understand the problem, how are you going to fix it? The two standard ways to do this are: (1) count first, save the result in a local, test against the local, and (2) remove the counter altogether, since it is unnecessary; instead, loop while the size is greater than zero. I prefer the latter solution; the fewer variables you mutate, the fewer mistakes you'll make in mutating them.

Upvotes: 11

wensveen
wensveen

Reputation: 884

It might have to do with the fact that your evaluation expression (i < sStack.size() + 1) is eveluated every iteration. Your stack shrinks every time while 'i' increments every time. You might want to save the stack's size in a variable and compare to that.

Ah, beaten to it by none other than Eric Lippert. I salute you, sir! :)

Upvotes: 0

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