C20 Answer

#include <stdio.h>
#include <stdlib.h>

/* Puzzle C20 -- determine if two integer arrays are equal
|
|  NOTE: one of these equal methods is wrong. Which one?
|
*/

int equal( int x[], int y[], int size )
{
  int j = 0;
  while ( j<size && x[j] == y[j] )
    j++ ;

  return j==size;
}

int equal2( int x[], int y[], int size )
{
  int j;
  for ( j=0; j<size; j++ )
    if ( x[j] != y[j] ) break;

  return j==size;
}

int equal3( int x[], int y[], int size )
{
  int j = 0;
  int equalSoFar = 1;

  while ( j<size && equalSoFar )
  {
    if ( x[j] != y[j] )
      equalSoFar = 0;
    else
      j++ ;
  }

  return equalSoFar;
}

int equal4( int x[], int y[], int size )
{
  int j = 0;

  while( j<size && x[j]==y[j++ ] ) ;

  return j>=size ;
}

void fillArrayInOrder( int arr[], int size, int start )
{
  int j;
  
  for ( j=0; j<size; j++ )
  {
    arr[j] = j+start;
  }
}

void printArray( int arr[], int size )
{
  const int N = 10;
  int j;
  
  for ( j=0; j<size; j++ )
  {
    if ( j%N == N-1 )
      printf("%4d\n", arr[j] );
    else
      printf("%4d ", arr[j] );    
  }
}

int main(int argc, char *argv[])
{
  const int SIZE = 30;
  int x[ SIZE ], y[ SIZE ];
  
  fillArrayInOrder( x, SIZE, 0 );
  fillArrayInOrder( y, SIZE, 0 );
  x[SIZE-1] = -99;

  printf("\nx:\n");
  printArray( x, SIZE );
  printf("\n\ny:\n");
  printArray( y, SIZE );

  if ( equal( x, y, SIZE ) )
    printf("\n\nArrays are equal\n");
  else
    printf("\n\nArrays are NOT equal\n");

  if ( equal2( x, y, SIZE ) )
    printf("\n\nArrays are equal\n");
  else
    printf("\n\nArrays are NOT equal\n");

  if ( equal3( x, y, SIZE ) )
    printf("\n\nArrays are equal\n");
  else
    printf("\n\nArrays are NOT equal\n");

  if ( equal4( x, y, SIZE ) )
    printf("\n\nArrays are equal\n");
  else
    printf("\n\nArrays are NOT equal\n");

  printf("\n\n");
  system("PAUSE");	
  return 0;
}

Comments: This program implements an equal() method in four different ways. Possibly the first equal() function is the best in terms of clarity, but a case could be made for some of the others. Notice how all functions but the second make use of the short-circuit operation of the && operator.

However, one of the methods is NOT correct. See if you can figure out which one is incorrect without running the program. This might give you some insight into coding clarity.