Question

I have an assignment (i think a pretty common one) where the goal is to develop a LargeInteger class that can do calculations with.. very large integers.

I am obviously not allowed to use the Java.math.bigeinteger class at all.

Right off the top I am stuck. I need to take 2 Strings from the user (the long digits) and then I will be using these strings to perform the various calculation methods (add, divide, multiply etc.)

Can anyone explain to me the theory behind how this is supposed to work? After I take the string from the user (since it is too large to store in int) am I supposed to break it up maybe into 10 digit blocks of long numbers (I think 10 is the max long maybe 9?)

any help is appreciated.

Answer 1

First off, think about what a convenient data structure to store the number would be. Think about how you would store an N digit number into an int[] array.

Now let’s take addition for example. How would you go about adding two N digit numbers?

Using our grade-school addition, first we look at the least significant digit (in standard notation, this would be the right-most digit) of both numbers. Then add them up.

So if the right-most digits were 7 and 8, we would obtain 15. Take the right-most digit of this result (5) and that’s the least significant digit of the answer. The 1 is carried over to the next calculation. So now we look at the 2nd least significant digit and add those together along with the carry (if there is no carry, it is 0). And repeat until there are no digits left to add.

The basic idea is to translate how you add, multiply, etc by hand into code when the numbers are stored in some data structure.