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  1. #include <iostream>
  2.  
  3. int EncryptDecrypt( int Number , bool Encrypting = true ); //you can use std::string also
  4. void Swap( int Container[] , int ElementOneOffset , int ElementTwoOffset ); //swapping two elements
  5.  
  6. int main()
  7. {
  8. 	int number;
  9. 	while( std::cout << "Please enter a 4 digit number to encrypt: " && std::cin >> number
  10. 	&& number < 1000 && number > 9999 )
  11. 	{
  12. 		std::cout << "Invalid number: " << number << " is not greater than 999 or less than 10000"
  13. 		<< std::endl;
  14. 	}
  15.  
  16. 	int Encrypted = EncryptDecrypt( number );
  17. 	int Decrypted = EncryptDecrypt( Encrypted , false ); //we could simply assign to number
  18. 	//but we wish to test the decrypt function
  19.  
  20. 	std::cout << "Starting: " << number << std::endl;
  21. 	std::cout << "Encrypted: " << Encrypted << std::endl;
  22. 	std::cout << "Decrypted: " << Decrypted << std::endl;
  23.  
  24. 	return 0;
  25. }
  26.  
  27. int EncryptDecrypt( int Number , bool Encrypting )
  28. {
  29. 	const int Digits = 4; //4 digit long number
  30. 	const int Base = 10; //we are using decimal base
  31. 	int ReverseDigits[Digits]; //the digits stored in reverse order --will be the e
  32. 	int Digit = Number  % Base; //this will be p and set to right digit of number
  33. 	int CurrentDigit = 0; //current digit we on , offset of ReverseDigits array
  34. 	int Increment = 7; //default is encrypt
  35. 	int Result = 0; //result we return
  36. 	int Multiplier = 1; //multiplier to the current digit same as 10^digit-1
  37.  
  38. 	if( !Encrypting ) //decrypting
  39. 		Increment = -Increment;
  40.  
  41. 	if( Number < 1000 && Number ) //less than 1000 but not0
  42. 	{
  43. 		int Temp = Number;
  44. 		int TempOffset = Digits - 1;
  45.  
  46. 		while( Temp < 1000 )
  47. 		{
  48. 			ReverseDigits[TempOffset--] = (Increment + Base) % Base; //Digit == 0
  49. 			Temp *= Base;
  50. 		}
  51. 	}
  52. 	else  //Number == 0
  53. 	{
  54. 		for( int Offset = 0; Offset < Digits; ++Offset )
  55. 		{
  56. 			ReverseDigits[Offset] = (Increment + Base) % Base; //Digit == 0
  57. 		}
  58.  
  59. 	}
  60.  
  61. 	while( Number ) //loop while there are digits left ( Number != 0 )
  62. 	{
  63. 		Digit = Number % Base; //Get the next digit
  64. 		Number /= Base; //Remove the last digit
  65. 		ReverseDigits[CurrentDigit++] = ( Digit + Increment + Base) % Base;
  66. 		//We must Add base incase of a negative number while decrypting.
  67. 		//increment current digit
  68. 	}
  69.  
  70. 	//Current order is 4321 we wish to have order 2143 so we must swap a few
  71.  
  72. 	Swap( ReverseDigits , 0 , 2 ); //Swap ReverseDigits[0] with ReverseDigits[2];
  73. 	Swap( ReverseDigits , 1 , 3 ); //Swap ReverseDigits[1] with ReverseDigits[3];
  74.  
  75.  
  76. 	for( int digit = 0; digit < Digits; ++digit )
  77. 	{
  78. 		Result += ReverseDigits[digit] * Multiplier;
  79. 		Multiplier *= Base;
  80. 	}
  81.  
  82. 	return Result;
  83.  
  84. }
  85.  
  86. void Swap( int Container[] , int ElementOneOffset , int ElementTwoOffset )
  87. {
  88. 	int temp = Container[ElementOneOffset];
  89. 	Container[ElementOneOffset] = Container[ElementTwoOffset];
  90. 	Container[ElementTwoOffset] = temp;
  91. }
Success #stdin #stdout 0s 3300KB
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stdin
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1234
stdout
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Please enter a 4 digit number to encrypt: Starting: 1234
Encrypted: 189
Decrypted: 1234
https://ideone.com/5aTkAU
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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