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  1. #include <iostream>
  2. #include <string>
  3.  
  4. using namespace std;
  5.  
  6. class BigInteger
  7. {
  8. 	friend ostream& operator<<(ostream&, const BigInteger&);
  9.  
  10. public:
  11. 	BigInteger() = default;
  12. 	BigInteger(string);
  13. 	~BigInteger() = default;
  14. 	BigInteger(const BigInteger&);
  15. 	BigInteger& operator=(const BigInteger&);
  16.  
  17. 	BigInteger& operator+(BigInteger&);
  18. 	BigInteger& operator-(BigInteger&);
  19. 	BigInteger& operator*(const BigInteger&);
  20.  
  21. private:
  22. 	string num;
  23. };
  24.  
  25. BigInteger& BigInteger::operator*(const BigInteger& rhs)
  26. {
  27. 	string tmp(num.length() + rhs.num.length(), '0');
  28. 	//a string in which I'll be temporarily storing the result
  29. 	unsigned char carry = '0';
  30. 	int d = 0;
  31. 	//I'll use this to move with one index to the left in the result 
  32. 	for (int i = num.length() - 1; i >= 0; --i)
  33. 		//start with the multiplying from the end of the first number
  34. 	{
  35. 		carry = '0';
  36. 		for (int j = rhs.num.length() - 1, z = tmp.length() - 1 - d; j >= 0; --j, --z)
  37. 			//start with the multiplying from the end of the second number and begin filling the result string (again from the end)
  38. 		{
  39. 			int res = ((tmp[z] - '0') + (num[i] - '0') * (rhs.num[j] - '0') + (carry - '0'));
  40. 			carry = (res / 10) + '0';
  41. 			tmp[z] = (res % 10) + '0';
  42. 			if (j == 0)
  43. 			{
  44. 				tmp[z - 1] = carry;
  45. 			}
  46. 		}
  47. 		++d;
  48. 	}
  49. 	if (carry != '0')
  50. 	{
  51. 		tmp[0] = carry;
  52. 	}
  53. 	else
  54. 	{
  55. 		tmp.erase(0, 1);
  56. 	}
  57. 	num = tmp;
  58. 	return *this;
  59. }
  60.  
  61. ostream& operator<<(ostream& out, const BigInteger& rhs)
  62. {
  63. 	out << rhs.num;
  64. 	return out;
  65. }
  66.  
  67. BigInteger::BigInteger(string num)
  68. :num(num)
  69. {}
  70.  
  71. int main()
  72. {
  73. 	BigInteger num3("6789");
  74. 	BigInteger num4("9876");
  75. 	cout << num3 <<"*" << num4 << endl;
  76. 	cout << num3 * num4 << endl;
  77. 	cout <<endl;
  78. 	cout << 6789 * 9876 << endl;
  79.  
  80. 	return 0;
  81. }
Success #stdin #stdout 0s 4360KB
comments ()
stdin 
Standard input is empty
stdout 
6789*9876
67048164

67048164
https://ideone.com/0mAvwE
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
secret

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