How to add, subtract, multiply and divide 2 numbers each containing 100 digits in C? (using arrays)

Question

I'am trying to write a C code to add, subtract, multiply and divide 2 numbers each containing 100 digits. This should include the use of arrays.

Can anyone please give me any suggestions, a pseudo code or a sample code? To be more clear The user will enter 2 numbers(Integers) Each number can comprise of 100 or less digits i.e integer a can be 10 or 234 or 43582 or 23456788 or 23445667788...... etc. Same for integer b. Now taking these two integers I have to perform the arithmetic operations of Addition,Subtraction,Division,Multiplication,Modulas(%)

@brunch875 which standard data type in C can store a 100 digit number? I think none. He wants to implement something like BigInt himself and asks for pointers as to how to get started. — rfreytag, Oct 11 '15 at 10:36
For multiplication you can use the Karatsuba algorithm: https://en.wikipedia.org/wiki/Karatsuba_algorithm Addition should be fairly easy, just have to carry over the carry bit to the next array element. — rfreytag, Oct 11 '15 at 10:39
@brunch875 try fitting a 100-digit number in a data type in C — Guillaume, Oct 11 '15 at 10:45
@Guillaume: According to Henry F, you can fit any number of digits in an `int` type, as long as they are all leading zeroes. — chqrlie, Oct 11 '15 at 10:51

score 3 · Answer 1 · edited May 23 '17 at 12:08

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You could try using the GMP Library as answered in this question. It can perform Bigint operations in both C and C++. Also if you are fine with C++ code for Bigint you could check out this blogpost.

edited May 23 '17 at 12:08

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answered Oct 11 '15 at 10:53

Rahul Nori

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hi Rahul,can you explain this a bit more please.What is the GMP Library used for?? – caitan correia Oct 12 '15 at 14:25
@caitancorreia try this [pdf](http://www-oldurls.inf.ethz.ch/personal/fukudak/lect/mssemi/reports/01_rep_DiyoraSalimova.pdf). Please search some more about it, i am sure you will find what you want to know. – Rahul Nori Oct 12 '15 at 16:58

score 1 · Answer 2 · answered Oct 11 '15 at 10:53

You are looking for hints on implementing arbitrary precision arithmetic. Start be reading this article: https://en.wikipedia.org/wiki/Arbitrary-precision_arithmetic , then search for bignum c code with a search engine, sample implementations are easy to find. Avoid full blown packages such as gnu MP because they are too advanced and not the right starting point.

How to add, subtract, multiply and divide 2 numbers each containing 100 digits in C? (using arrays)

2 Answers2