What is root? what can it do? where can i get it for an android tablet 5.1 lollipop version without a virus or anything? is it worth doing a root?

Write a program that begins by reading in a series of positive integers on a single line of input and then computes and prints the product of those integers. integers are accepted and multiplied until the user enters an integer less than 1. this final number is not part of the product. then, the program prints the product. if the first entered number is negative or 0, the program must print “bad input.” and terminate immediately