I haven’t analyzed what your code is doing but I can tell you the difference between == and =.
== is an equality comparison operator. It allows to check if the left hand side and the right hand side are equal, in which case it returns the boolean value true otherwise false.
=, on the other hand, is an assignment operator. It allows you to give the value on the right-hand side to a variable on the left-hand side. So the compiler is right here in warning you that '==': operator has no effect; did you intend '='?
Therefore, inside your do {...} while loop you should be using = statements instead of ==.
solved Is it possble to convert a number to decimal base ten using do while? [closed]