Inserting at the end of stack

user_6455600 0
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static void insert_at_bottom(char x){

    if(st.isEmpty())
        st.push(x);

    else{
        /* All items are held in Function Call Stack until we
           reach end of the stack. When the stack becomes
           empty, the st.size() becomes 0, the
           above if part is executed and the item is inserted
           at the bottom */

        char a = st.peek();
        st.pop();
        insert_at_bottom(x);

        //push all the items held in Function Call Stack
        //once the item is inserted at the bottom
        st.push(a);
    }
}

In the above code, I have a question about this step:

if(st.isEmpty())
        st.push(x);

Don't we require a return statement after st.push(x)?

I mean that in recursion stack when that condition is satisfied i.e. when the stack is empty, it would push x into the stack, but how would it return to the previous call without the return statement?

return recursion java
9 Answers
if(st.isEmpty()){
  st.push(x);
  return;
}

I think we should add a return after adding the element because writing just return means control back cursor to calling function without executing futhure code. and because of the recursion we need a base case also

user_114511300

No, you don't necessarily require a return statement as there are no statements in the if block after

if(st.isEmpty()) st.push(x);

is executed.

The code will perform the same whether we write a return statement or not.

user_148080200

There are two reasons why return is not required.

  1. Since the function is of type void we do not need to return anything.

  2. In case you are thinking that after if(st.isEmpty()) st.push(x); remaining part of code will execute then there is else part which will not execute and hence recursion stack will automatically return to the previous call;

user_137067520

Here we will not require any return statement as we know, the recursion call return there where it was called... char a = st.peek(); st.pop(); insert_at_bottom(x); st.push(a);

In this case, insert _at_ bottom(x) will call itself and will return until it reaches its base case.

user_149579640

if you are using C/C++/java, you can add a return statement that is returning essentially nothing (because the prototype or the return type of function insert_at_bottom is void), like:

if(st.isEmpty())
{
  st.push(x);
  return;
}

However, I must point out that since you are using the if...else statement, the flow of control would itself return from the current function-call-stack even if you don't use a return statement because after executing the if or else statement, the control would reach at the end of the function.

user_135220560

You must have added return statement in the base case. But here..

Since all the other code is in else statement, base case will skip all of that and reach the end of the code anyways, forcing it to return automatically.

user_163918410

return keyword is not used because the algorithm is in if else block . When the stack is empty than the if part is evaluated and else is not evaluated. Then the control goes after the else statement. There are no statements to execute after else block so automatically algorithm returns.

Even if you write 'return' keyword after if-else block the output would be same. Also if return type is void and you not write 'return' keyword than automatically the call would be over after the control reaches to end of the algorithm and the call returns;

user_166218910

Why we don't need a return statement is because:

  1. The stack.push(x) is inside if block and thus the execution will not go in the else block and will return back to the previous call after this statement.
  2. Also this looks like a code in java. And in java the Stack object's reference is passed as value in function call. So during recursion call as the values are being pushed and popped, the stack will automatically keep on updating. So need need to return any stack object also.
user_96658660
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