行番号の表示切替 行折り返しの切替 
  1.  /* A little algorithmic adventure in math,
  2.  // Greatest common denominator/divisor.
  3.  //
  4.  // Note that this does not attempt to properly handle negative numbers 
  5.  // beyond what strtoul() does. 
  6.  // (When did strtoul() start "casting" negatives to positive?)
  7.  //
  8.  // If anyone hassles me about Intellectual Property on this, 
  9.  // I'll hit them over the head with a copy of Euclid, and again with　a copy of Knuth.
  10.  // Joel Rees, Amagasaki, March 2015
  11.  */
  12.  
  13.  
  14.  #include <stdio.h>
  15.  #include <stdlib.h>
  16.  
  17.  
  18.  long gcd( long numA, long numB )
  19.  {
  20.     long temp;
  21.  
  22.     while ( numA != numB )
  23.     {
  24.        if ( numA < numB )
  25.        {
  26.           temp = numA;
  27.           numA = numB;
  28.           numB = temp; 
  29.        }
  30.        numA -= numB;
  31.     }
  32.     return numA;
  33.  }
  34.  
  35.  
  36.  int main( int argc, char * argv[] )
  37.  {
  38.     long n1, n2;
  39.     char * parseP;
  40.     long divisor;
  41.  
  42.     if ( argc != 3 )
  43.     {  printf( "usage: %s <numA> <numB>\n",
  44.                argv[ 0 ] );
  45.        puts( "\tto calculate the greatest common divisor\n\tof two unsigned numbers." );
  46.        return EXIT_FAILURE;
  47.     }
  48.  
  49.     n1 = strtoul( argv[ 1 ], &parseP, 0 );
  50.     if ( parseP > argv[ 1 ] )
  51.     {
  52.        n2 = strtoul( argv[ 2 ], &parseP, 0 );
  53.        if ( parseP > argv[ 2 ] )
  54.        {
  55.           divisor = gcd( n1, n2 );
  56.           printf( "greatest common divisor: %ld\n", divisor );
  57.           printf( "%ld/%ld => %ld/%ld\n", n1, n2, n1 / divisor, n2 / divisor );
  58.           return EXIT_SUCCESS;
  59.        }
  60.        else
  61.        {
  62.           printf( "%s is not an unsigned number I can recognize.\n", argv[ 2 ] );
  63.        }
  64.     }
  65.     else
  66.     {
  67.        printf( "%s is not an unsigned number I can recognize.\n", argv[ 1 ] );
  68.     }
  69.     return EXIT_FAILURE;
  70.  }