runtime error

[samarth123]

#include "bits/stdc++.h"
#include<stack>
using namespace std;
int main()
{
	while(true)
	{
		int n;
		cin>>n;
		int a[n];
		stack<int> st;
		if(n==0)break;
		else		
		{
			for(int i=0;i<n;i++)
			{
				cin>>a[i];
			}
		 
		 int count=1;
		 for(int i=0;i<n;i++)
		 {
		 	st.push(a[i]);
			 while(st.top()==count)
		 	{
		 	count++;
			 st.pop();	
			}
//			st.push(a[i]);
		 }
		 if(st.size()==0)
		 {
		 	cout<<"yes\n";
		 }
		 else cout<<"no\n";
	    }    
	}
}

WEll what is the error in this code.I am not able to figure out..It is showing runtime error.

[Moschops]

I see two problems.

Firstly, in C++, a variable length array ( int a[n]; ) is forbidden.

Secondly, on line 24, you call top on an empty stack. This is bad. Do not do this. First check that the stack isn't empty, and only then call top on it.

[TarikNeaj]

I'm surprised this even compiles.

cin>>n;
int a[n];

This doesn't work in c++. The size of an array must be constant at compile time.
You can only do it that way if you allocate memory on the heap for it.

cin>>n;
int *a = new int[n];

But you'll have to use delete so you don't get memory leak - http://www.cplusplus.com/doc/tutorial/dynamic/

The best thing to do, is to just use std::vector - http://www.cplusplus.com/reference/vector/vector/vector/

[samarth123]

Well i got the mistake in the stack which you mentioned .But there is no problem in the array because i have taken the input of variable n then i have defined the array a.
thanks

[Moschops]

It's still illegal in C++. Your compiler is letting you create a variable length array. It shouldn't. It's illegal. It's not C++. It's incorrect C++. Your compiler might let you do it, but it shouldn't. You shouldn't write incorrect code just because the compiler you're happening to use right now happens to let you.

[samarth123]

Okk !!thanks for the advice @Moschops