Handling large numbers in C++?

Question

What is the best way to handle large numeric inputs in C++ (for example 10^100)?

For algorithms I usually switch over to ruby and I sometimes use strings.

Any other good methods?

Answer 1

It sounds like you're looking for a way to enter Arbitrary Precision numbers. here are two libraries you could use: GMP and MAPM

Answer 2

Check out The Large Integer Case Study in C++.pdf by Owen Astrachan. I found this file extremely useful with detail introduction and code implementation. It doesn't use any 3rd-party library. I have used this to handle huge numbers (as long as you have enough memory to store vector<char>) with no problems.

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Idea: It implements an arbitrary precision integer class by storing big int in a vector<char>.

vector<char> myDigits; // stores all digits of number 

Then all operations related to the big int, including <<, >>, +, -, *, ==, <, !=, >, etc., can be done based on operations on this char array.

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Taste of the code: Here is the header file, you can find its cpp with codes in the pdf file.

#include <iostream> #include <string> // for strings #include <vector> // for sequence of digits using namespace std;  class BigInt { public:     BigInt(); // default constructor, value = 0     BigInt(int); // assign an integer value     BigInt(const string &); // assign a string     // may need these in alternative implementation     // BigInt(const BigInt &); // copy constructor     // ~BigInt(); // destructor     // const BigInt & operator = (const BigInt &);     // assignment operator     // operators: arithmetic, relational     const BigInt & operator += (const BigInt &);     const BigInt & operator -= (const BigInt &);     const BigInt & operator *= (const BigInt &);     const BigInt & operator *= (int num);     string ToString() const; // convert to string     int ToInt() const; // convert to int     double ToDouble() const; // convert to double     // facilitate operators ==, <, << without friends     bool Equal(const BigInt & rhs) const;     bool LessThan(const BigInt & rhs) const;     void Print(ostream & os) const; private:     // other helper functions     bool IsNegative() const; // return true iff number is negative     bool IsPositive() const; // return true iff number is positive     int NumDigits() const; // return # digits in number     int GetDigit(int k) const;     void AddSigDigit(int value);     void ChangeDigit(int k, int value);     void Normalize();     // private state/instance variables     enum Sign{positive,negative};     Sign mySign; // is number positive or negative     vector<char> myDigits; // stores all digits of number     int myNumDigits; // stores # of digits of number };  // free functions ostream & operator <<(ostream &, const BigInt &); istream & operator >>(istream &, BigInt &); BigInt operator +(const BigInt & lhs, const BigInt & rhs); BigInt operator -(const BigInt & lhs, const BigInt & rhs); BigInt operator *(const BigInt & lhs, const BigInt & rhs); BigInt operator *(const BigInt & lhs, int num); BigInt operator *(int num, const BigInt & rhs); bool operator == (const BigInt & lhs, const BigInt & rhs); bool operator < (const BigInt & lhs, const BigInt & rhs); bool operator != (const BigInt & lhs, const BigInt & rhs); bool operator > (const BigInt & lhs, const BigInt & rhs); bool operator >= (const BigInt & lhs, const BigInt & rhs); bool operator <= (const BigInt & lhs, const BigInt & rhs);