Member Avatar for kartik14

Hi,

Is there any way to store huge numbers (for example, a number with a million digits) in a C program and be able to perform operations on it ?

Thanks..

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  • Latest Post Latest Post by ivailosp

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raised the core question (million-digit integers). As pointed out, a hand-rolled string-based implementation is possible for learning purposes; as noted, production work at that scale is best done with a battle-tested arbitrary-precision library. Libraries manage limb-based storage, avoid O(n^2) traps, and switch to fast multiplication algorithms (Karatsuba, Toom-Cook, Schonhage-Strassen) when needed. See the GMP manual and the Boost.Multiprecision cpp_int docs for concrete APIs.

A minimal C++ example using Boost.Multiprecision (convenient, header-only) shows usage patterns:

#include <boost/multiprecision/cpp_int.hpp>
#include <iostream>
#include <string>

using boost::multiprecision::cpp_int;

int main() {
    std::string s = /* load million-digit decimal string */;
    cpp_int n = 0;
    for (char c : s) n = n * 10 + (c - '0'); // simple conversion
    cpp_int r = n * n; // example operation
    std::cout << r << '\n';
    return 0;
}

Practical notes: a million decimal digits in text is ~1 MB; in binary it is about 3.322e6 bits (~0.4 MB). Naive O(n^2) multiplication on such sizes is impractical—use libraries that provide FFT-based multiplication. For best throughput, prefer GMP for heavy work (and its mpz_import for fast binary imports), parse/print in large chunks, and test/profile on smaller scales before scaling up.

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Member Avatar for ivailosp

using std::string and operator overloading, yes it is able

Member Avatar for kartik14

Hi, thanks for your reply..

Can you elaborate the procedure.. It would be very helpful if you could post a link with the mentioned approach...

Thanks :)

Member Avatar for ArkM

There are tons of freeware libraries to perform ops over arbitrary precision numbers in C and C++. Search Google for "C arbitrary precision numbers library". For example:

It's not so easy to invent a new library in this area...

Member Avatar for ivailosp 
string num1 = "1234";
string num2 = "4567";
string sum = "";
char tmp2 = 0;
1. reverse num1 and num2
2. for 0 to string size() do 
char tmp = num1[i] + num2[i] + tmp2;
tmp2 = 0;
if (tmp > '9'){
  tmp-=10;
  tmp2 = 1;
}
sum+=tmp;

3. reverse sum and that's it :)

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