big_int

big_int is an implementation of big integer library in C++

Contents

• Overview
• Usage
• Features
• Insights
• Contributing
• License

Overview

• big_int is a header-only library for working with integer values larger than the C++ built-in data types
• Simple to get started. Simply download the header file, include it in your code and start using the library
• No additional dependencies required
• Works well with modern versions of C++ (C++11 / C++14 / C++17)

Usage

Getting started

Download the header file to any location in your project folder. Then #include it in your code depending upon where you put the file :

#include "big_int.hpp"

or

#include "folder_name/big_int.hpp"

Creating objects

An object of the big_int class can be instantiated in multiple ways :

// default value
big_int a;                             // 'a' gets the value 0

// 'int' as an argument
big_int b(49);                         // 'b' gets the value 49

// 'long long' as an argument
// Make sure value fits in long long
big_int c(-9223372036854775808);       // 'c' gets the value -9223372036854775808

// 'std::string' as an argument
big_int d("9223372036854775899");      // 'd' gets the value 9223372036854775899

// using the assignment operator
big_int e = -49;                       // 'e' gets the value -49
big_int f = 9223372036854775807;       // 'f' gets the value 9223372036854775807
big_int g = std::string("98765432198");// 'g' gets the value 98765432198 

Features

Operators

• Assignment : =

  An instance can be assigned value using the assignment = operator. The second operand can be either a big_int, an integer (fitting in the long long range), or a std::string.

  a = 987654;
  b = std::string("123456789");
  b = a;
  
  std::string str = "123456";
  a = str;

• Increment and decrement : ++, --

  // pre-increment/decrement
  big_int a = 1;
  big_int b = ++a;        // a = 2, b = 2
  b = --a;                // a = 1, b = 1
  
  //post-increment/decrement
  big_int c = 1;
  big_int d = c++;        // c = 2, d = 1
  d = c--;                // c = 1, d = 2

• Arithmetic : +, -, *, /, %

  Both the operands must be instances of the big_int class.

  big_int a("987654321987654321");
  big_int b("123456789123456789");
  
  big_int c = a + b;        // c = 1111111111111111110
  big_int d = a - b;        // d = 864197532864197532 
  big_int e = a * b;        // e = 121932631356500531347203169112635269
  big_int f = a / b;        // f = 8
  big_int g = a % b;        // g = 9000000009

• Arithmetic - assignment : +=, -=, *=, /=, %=

  Both the operands must be instances of the big_int class.

  big_int a("987654321987654321");
  big_int b(123456789);
  a += b;                 // a = 987654322111111110
  a -= b;                 // a = 987654321987654321
  a *= b;                 // a = 121932631234567900112635269
  a /= b;                 // a = 987654321987654321
  a %= b;                 // a = 111111201

• Relational / Comparison : ==, !=, >=, <=, >, <

  Both the operands must be instances of the big_int class.

  big_int a(12345);
  big_int b(54321);
  big_int c(98765);
  
  if(a >= b || b != c || a > c) {...}
  if(b == c && a <= b && a < c) {...}

• I/O stream : >>, <<

  big_int a, b;
  std::cin >> a >> b;
  std::cout << a << " " << b << std::endl;

Instance methods

• .absolute()

  Returns the absolute value of an instance.

  big_int a(-49);
  big_int b = a.absolute();       // b = 49

• .digit_count()

  Returns the number of digits in an instance.

  big_int a(12345), b(-1234), c("-0000023");
  std::cout << a.digit_count();    // 5
  std::cout << b.digit_count();    // 4
  std::cout << c.digit_count();    // 2

• .multiply_10(int count)

  Returns a big_int instance with the value equals value of the current instance multiplied by 10, count times. If count is not specified, then its value is taken as 1. This is much faster than multiplying using the * operator.

  big_int a(1234);
  big_int b = a.multiply_10(5);      // b = 123400000
  big_int c = a.multiply_10();       // c = 12340

• .divide_10(int count)

  Returns a big_int instance with the value equals value of the current instance divided by 10, count times. If count is not specified, then its value is taken as 1. This is much faster than dividing using the / operator.

  big_int a(123456);
  big_int b = a.divide_10(4);      // b = 12
  big_int c = a.divide_10();       // c = 12345

• .fits_in_ll()

  Returns whether an instance lies in the range of long long or not.

  big_int a("9223372036854775807");
  big_int b("-9223372036854775809");
  std::cout << a.fits_in_ll();      // 1
  std::cout << b.fits_in_ll();      // 0

• .is_zero()

  Returns whether the value of an instance is 0 or not.

  big_int a;
  big_int b(1);
  std::cout << a.is_zero();        // 1
  std::cout << b.is_zero();        // 0 

Insights

• An instance can be printed by using the output stream std::cout <<, but the .print() instance method can also be used.

• An instance can be taken input by using the input stream std::cin >>, but the .read() instance method can also be used.

• Arithmetic operations can also be done by using instance methods upon the object which is left operand of the operation. +, -, *, / and % can be performed by .add(big_int), .subtract(big_int), .multiply(big_int), .divide(big_int) and .modulo(big_int) respectively.

• The .set_value() instance method can also be used an alternative to the assignment = operator by passing the right operand as the argument.

• Multiplication is implemented using the traditional slow multiplication algorithm and a faster Karatsuba multiplication algorithm. The feasible one is used depending upon the operands.

• As of now, the modulo % method does not returns the correct result for negative integers which are out of the long long range.

Contributing

Contributions are welcome. Fork this repository, make the desired changes, open a pull request or an issue. Make sure your changes does not introduce any bugs and all the tests are passing.

License

This project is licensed under the terms of MIT License.