While Loop Problem

I'm recently starting my learning for the PLSQL programs. So I executed a simple PLSQL pogram with the use of simple and For loop But failed for while loop.

But while executing this PlSQL program it was showing me plsql program executed successfully but the result did not came out.

So My point is why the output was not coming. same code is giving o/p for simple and For loop.

So Can you please anyone tell me the reason behind this.

Thanks in Advance