C++ :: Bigint - Global Constant Size

I am making a class called "bigint" and i have to have a global constant "size". How do I make that global "size" the size of bigint? If "size" is an array and "bigint" is an object how does that work? Heres the instructions for the program..

Requirements:
-You must use the class construct to implement your ADT.
-The ADT bigint need only work for positive numbers.
-Use a global constant value for the maximum size of the bigint that is, a constant sized array.

Implementation:
-The size of the bigint must be specified by a global constant
-A method (constructor) to initialize a bigint to zero.
-A method (constructor) to initialize a bigint to an int value you provide [0, maxint]. Example: bigint(128).
-A method (constructor) to initialize a bigint to a char[] you provide. You can assume what is provided is a valid bigint. Example: bigint("299793").
-A method to write a bigint that prints at most 60 digits per line.
-A method to compare if two bigints are equal. It should return a bool - true if equal and false otherwise.