C++ program, the program runs even the input range exits its limit, how?

In fibonacci series C++ program, if we are getting the input as a [50], the program even runs for a[100] or more, how come?

C++ program, the program runs even the input range exits its limit, how?
post the program plz


and i think u have an error in the loop condition


note:Fibonacci series is much easier using recursive method " maybe it's not effective but easier"