luhn.cpp

# include <cmath>
# include <cstdlib>
# include <cstring>
# include <ctime>
# include <iomanip>
# include <iostream>

using namespace std;

# include "luhn.hpp"

//****************************************************************************80

bool ch_is_digit ( char ch )

//****************************************************************************80
//
//  Purpose:
//
//    CH_IS_DIGIT returns TRUE if a character is a decimal digit.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    10 September 2015
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, char CH, the character to be analyzed.
//
//    Output, bool CH_IS_DIGIT, is TRUE if the character is a digit.
//
{
  bool value;

  if ( '0' <= ch && ch <= '9' )
  {
    value = true;
  }
  else
  {
    value = false;
  }
  return value;
}
//****************************************************************************80

int ch_to_digit ( char ch )

//****************************************************************************80
//
//  Purpose:
//
//    CH_TO_DIGIT returns the integer value of a base 10 digit.
//
//  Example:
//
//     CH  DIGIT
//    ---  -----
//    '0'    0
//    '1'    1
//    ...  ...
//    '9'    9
//    ' '   -1
//    'X'   -1
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    10 September 2015
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, char CH, the decimal digit, '0' through '9' are legal.
//
//    Output, int CH_TO_DIGIT, the corresponding integer value.  If the
//    character was 'illegal', then DIGIT is -1.
//
{
  int value;

  if ( '0' <= ch && ch <= '9' )
  {
    value = ch - '0';
  }
  else
  {
    value = -1;
  }

  return value;
}
//****************************************************************************80

void i4vec_print ( int n, int a[], string title )

//****************************************************************************80
//
//  Purpose:
//
//    I4VEC_PRINT prints an I4VEC.
//
//  Discussion:
//
//    An I4VEC is a vector of integer values.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    30 August 2009
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, int N, the number of components of the vector.
//
//    Input, int A[N], the vector to be printed.
//
//    Input, string TITLE, a title to be printed first.
//    TITLE may be blank.
//
{
  int i;

  cout << "\n";
  cout << title << "\n";
  cout << "\n";
  for ( i = 0; i <= n-1; i++ )
  {
    cout << setw(6) << i + 1 << "  "
         << setw(8) << a[i]  << "\n";
  }

  return;
}
//****************************************************************************80

int luhn_check_digit_calculate ( string s )

//****************************************************************************80
//
//  Purpose:
//
//    LUHN_CHECK_DIGIT_CALCULATE determines the Luhn check digit of a string.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    11 September 2015
//
//  Reference:
//
//    https://en.wikipedia.org/wiki/Luhn_algorithm
//
//  Parameters:
//
//    Input, string S, the string of digits to be checked.
//
//    Output, integer LUHN_CHECK_DIGIT_CALCULATE, the Luhn check digit for 
//    this string.
//
{
  int s_len;
  string s2;
  int value;

  s_len = s.length ( );
  s2 = s + '0';

  value = luhn_checksum ( s2 );

  if ( value != 0 )
  {
    value = 10 - value;
  }

  return value;
}
//****************************************************************************80

int luhn_checksum ( string s )

//****************************************************************************80
//
//  Purpose:
//
//    LUHN_CHECKSUM determines the Luhn checksum of a string.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    11 September 2015
//
//  Reference:
//
//    https://en.wikipedia.org/wiki/Luhn_algorithm
//
//  Parameters:
//
//    Input, string S, the string of digits to be checked.
//
//    Output, int VALUE, is the Luhn checksum for this string.
//
{
  int d2;
  int *dvec;
  int i;
  int n;
  int value;
//
//  Count the digits in S.
//
  n = s_digits_count ( s );
//
//  Extract the digits from S.
//
  dvec = s_to_digits ( s, n );
//
//  Starting with the last-th digit, and going down by 2's, 
//  add the digit to the sum.
//
  value = 0;
  for ( i = n - 1; 0 <= i; i = i - 2 )
  {
    value = value + dvec[i];
  }
//
//  Starting with the next to the last digit, and going down by 2's, 
//  double the digit, and ADD THE DIGITS to the sum.
//
  for ( i = n - 2; 0 <= i; i = i - 2 )
  {
    d2 = 2 * dvec[i];
    value = value + ( d2 / 10 ) + ( d2 % 10 );
  }

  value = ( value % 10 );

  delete [] dvec;

  return value;
}
//****************************************************************************80

bool luhn_is_valid ( string s )

//****************************************************************************80
//
//  Purpose:
//
//    LUHN_IS_VALID determines whether a string with Luhn check digit is valid.
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    11 September 2015
//
//  Reference:
//
//    https://en.wikipedia.org/wiki/Luhn_algorithm
//
//  Parameters:
//
//    Input, string S, the string of digits to be checked.
//
//    Output, bool LUHN_IS_VALID, TRUE if the string is valid.
//
{
  int d;
  bool value;

  d = luhn_checksum ( s );

  if ( d == 0 )
  {
    value = true;
  }
  else
  {
    value = false;
  }
  
  return value;
}
//****************************************************************************80

int s_digits_count ( string s )

//****************************************************************************80
//
//  Purpose:
//
//    S_DIGITS_COUNT counts the digits in a string.
//
//  Discussion:
//
//    The string may include spaces, letters, and dashes, but only the
//    digits 0 through 9 will be counted.
//
//  Example:
//
//    S  => 34E94-70.6
//    N <=  7
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license. 
//
//  Modified:
//
//    09 September 2015
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, string S, the string.
//
//    Output, int S_DIGITS_COUNT, the number of digits.
//
{
  char c;
  int n;
  int s_len;
  int s_pos;

  s_len = s.length ( );

  s_pos = 0;
  n = 0;

  while ( s_pos < s_len )
  {

    c = s[s_pos];
    s_pos = s_pos + 1;

    if ( ch_is_digit ( c ) )
    {
      n = n + 1;
    }
  }

  return n;
}
//****************************************************************************80

int *s_to_digits ( string s, int n )

//****************************************************************************80
//
//  Purpose:
//
//    S_TO_DIGITS extracts N digits from a string.
//
//  Discussion:
//
//    The string may include spaces, letters, and dashes, but only the
//    digits 0 through 9 will be extracted.
//
//  Example:
//
//    S  => 34E94-70.6
//    N  => 5
//    D <=  (/ 3, 4, 9, 4, 7 /)
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license. 
//
//  Modified:
//
//    09 September 2015
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, string S, the string.
//
//    Input, int N, the number of digits to extract.
//
//    Output, int S_TO_DIGITS[N], the extracted digits.
//
{
  char c;
  int d;
  int d_pos;
  int *dvec;
  int s_len;
  int s_pos;

  dvec = new int[n];

  s_len = s.length ( );

  s_pos = 0;
  d_pos = 0;

  while ( d_pos < n )
  {
    if ( s_len <= s_pos )
    {
      cerr << "\n";
      cerr << "S_TO_DIGITS - Fatal error!\n";
      cerr << "  Could not read enough data from string.\n";
      exit ( 1 );
    }

    c = s[s_pos];
    s_pos = s_pos + 1;

    if ( ch_is_digit ( c ) )
    {
      d = ch_to_digit ( c );
      dvec[d_pos] = d;
      d_pos = d_pos + 1;
    }
  }

  return dvec;
}
//****************************************************************************80

void timestamp ( )

//****************************************************************************80
//
//  Purpose:
//
//    TIMESTAMP prints the current YMDHMS date as a time stamp.
//
//  Example:
//
//    31 May 2001 09:45:54 AM
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license.
//
//  Modified:
//
//    08 July 2009
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    None
//
{
# define TIME_SIZE 40

  static char time_buffer[TIME_SIZE];
  const struct std::tm *tm_ptr;
  size_t len;
  std::time_t now;

  now = std::time ( NULL );
  tm_ptr = std::localtime ( &now );

  len = std::strftime ( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm_ptr );

  std::cout << time_buffer << "\n";

  return;
# undef TIME_SIZE
}