How to reverse print stack using recursion?

Question

Please note that it is just reverse printing not reversing a stack

What I want to do is with the help of recursion print the stack i.e bottom to top printing.

I have tried myself but the result is not what I expected.My code looks like this.

#include <bits/stdc++.h>
using namespace std;


void print(stack<char>st){
   if(st.empty()){return;}
   st.pop();
   print(st);
   cout<<st.top();
}

 int main() {
    // Assume that I have stack already made....
    print(st);
    cout<<endl;
 }
 return 0;
}

Would anybody mind having pointing out my mistake ? Also when I pass stack by reference the results are unexpected.Thanks for support.

Runtime error is what it is showing me.In the above implementation.Thanks for looking :) @fractalwrench — behnc
– behnc, Commented May 29, 2016 at 8:08
stack<T> is designed to hide its implementation. You'd have to write your own stack based on a vector<T>, say. You're getting an error because when you pop the last element, the stack is empty, then you're trying to print st.top() which no longer exists. Move the cout to before the pop. — John D
– John D, Commented May 29, 2016 at 8:13
Your current implementation prints top to bottom, and stack<T> won't support what you want. You have to write your own MyStack class. Also, by calling pop you're removing the top of the stack - you may just want to print the stack without emptying it. — John D
– John D, Commented May 29, 2016 at 8:15

Mahedi Sabuj · Accepted Answer · 2016-05-29 09:04:04Z

3

Why don't you store the st.top() at variable and print it later.

void print(stack<char>st)
{
    if(st.empty())
    {
        return;
    }

    char top = st.top();
    st.pop();
    print(st);

    cout<<top<<endl;
}

Let me explain you:-

Suppose, Your stack --> 0, 1

Here, Call Hierarchy

print({0, 1}) { // stack after pop -- {0} print({0}) }
print({0}) { // stack after pop -- {} print ({}) // here you want to print top of empty stack // which gives the exception }

edited May 29, 2016 at 9:04

answered May 29, 2016 at 8:20

Mahedi Sabuj

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5 Comments

behnc Over a year ago

Why have you stored top ?

WhozCraig Over a year ago

@behnc because if you don't it is lost in the ether after the pop before the recursion (which is precisely the problem in your code).

Mahedi Sabuj Over a year ago

@behnc, see the example at the answer

behnc Over a year ago

Now I got it sir.Consider reverse printing of linked list.we need not to store any data in case of linked list because we are not deleting anything.But in case of stack we do delete by pop.So before we delete we store.Am I right sir ? @WhozCraig

WhozCraig Over a year ago

@behnc pop does exactly what its name implies: pops the top element from the stack. If it was the last element, then the stack is then empty. Afterward, invoking top() on an empty stack (as your code does) rears your exception. Mahedi's description is both accurate and worth of answer-selection. It describes in-detail what is going wrong.

Lalji Dhameliya · Accepted Answer · 2016-08-24 11:40:58Z

0

pop is function get element to print like reverse

 void printStack()
{
   if(!isEmpty())
   {
     int temp = pop();
     printStack();
     printf(" %d ", temp);
     push( temp);
   }
}

int pop() 
{
  if (isEmpty())
    printf("Stack is Empty...\n");
  else {
      st.top = st.top - 1;
      return st.array[st.top+1];
   }
}

answered Aug 24, 2016 at 11:40

Lalji Dhameliya

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