Declare a Big Integer in C++

Question

I am trying to run this algorithm in c++ in order to get a big number

#include<iostream>

using namespace std;
int main()
{
    int num,factorial=1;
    cout<<" Enter Number To Find Its Factorial:  ";

    cin>>num;

    for(int a=1;a<=num;a++)
    {
       factorial=factorial*a;
    }

    cout<<"Factorial of Given Number is ="<<factorial<<endl;
    return 0;
}

How can I declare a Big Integer like in Java instead of an int?

score 2 · Answer 1 · answered Aug 07 '15 at 00:59

There is no big-integer support in the C++ standard library. A common choice for big-number arithmetic is GMP. After downloading and installing the library, in your code you would #include <gmpxx.h> and declare mpz_class factorial instead of int factorial, then link against GMP.

Linking with GMP can be done in an IDE, by adding GMP in your editor’s compile settings; or by adding -lgmp to your compilation command (e.g., g++ or clang++).

score 0 · Answer 2 · answered Aug 07 '15 at 00:53

0

There is no arbitrary-precision arithmetic in c++ standard library. You'll need to implement it yourself using an array of integers, or use an existing non-standard library.

answered Aug 07 '15 at 00:53

eerorika

232,697
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So if I wanna declare a big integer I just add one of those libraries in my factorial class? i.e #include or whatnot? – Behrouz Hedayati Aug 07 '15 at 22:06
@BehrouzHedayati yes, you'll need to include the headers which define the types that you're going to use. – eerorika Aug 07 '15 at 23:37

score 0 · Answer 3 · answered Aug 07 '15 at 01:12

0

Try unsigned long long int for just convenience.

I just want to leave it as comment but I have low repu for commenting..

answered Aug 07 '15 at 01:12

Chickenchaser

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13

score 0 · Answer 4 · answered Aug 07 '15 at 01:44

There is no standard support for arbitrary-precision integers. However, a few libraries are available for handling big integers:

GNU MP Bignum Library
InfInt
C++ BigInt class
BigDigits multiple-precision arithmetic (in C)
BigIntegerCPP (only supports addition and multiplication)
C++ Big Integer Library (no longer maintained)

Declare a Big Integer in C++

4 Answers4