Doubt in fibonacci series

#1

Here’s my code - https://pastebin.pl/view/dd8899d1

Sometimes, we take a=0 & b=1 & sometimes we take both as 1, why?

Please explain me the concept and help me out with this.

#2

@gambhirrahul0 in Fibonacci series first term is always 0 and second is 1 but here you have used two terms a and b both starting from 1 it means they are not the first and second term just two variables to print the required answer.