fig06_19.c

C程序设计经典教程第5版程序示例,比较适合初级c语言的学生

/* Fig. 6.19: fig06_19.c
   Binary search of an array */
#include <stdio.h>
#define SIZE 15

/* function prototypes */
int binarySearch( const int b[], int searchKey, int low, int high );
void printHeader( void );
void printRow( const int b[], int low, int mid, int high );

/* function main begins program execution */
int main( void )
{
   int a[ SIZE ]; /* create array a */
   int i; /* counter for initializing elements 0-14 of array a */
   int key; /* value to locate in array a */
   int result; /* variable to hold location of key or -1 */

   /* create data */
   for ( i = 0; i < SIZE; i++ ) {
      a[ i ] = 2 * i;
   } /* end for */

   printf( "Enter a number between 0 and 28: " );
   scanf( "%d", &key );

   printHeader();

   /* search for key in array a */
   result = binarySearch( a, key, 0, SIZE - 1 );

   /* display results */
   if ( result != -1 ) {
      printf( "\n%d found in array element %d\n", key, result );
   } /* end if */
   else {
      printf( "\n%d not found\n", key );
   } /* end else */

   return 0; /* indicates successful termination */

} /* end main */

/* function to perform binary search of an array */
int binarySearch( const int b[], int searchKey, int low, int high )
{
   int middle; /* variable to hold middle element of array */

   /* loop until low subscript is greater than high subscript */
   while ( low <= high ) {

      /* determine middle element of subarray being searched */
      middle = ( low + high ) / 2;

      /* display subarray used in this loop iteration */
      printRow( b, low, middle, high );

      /* if searchKey matched middle element, return middle */
      if ( searchKey == b[ middle ] ) {
         return middle;
      } /* end if */

      /* if searchKey less than middle element, set new high */
      else if ( searchKey < b[ middle ] ) {
         high = middle - 1; /* search low end of array */
      } /* end else if */

      /* if searchKey greater than middle element, set new low */
      else {
         low = middle + 1; /* search high end of array */
      } /* end else */

   } /* end while */

   return -1;   /* searchKey not found */

} /* end function binarySearch */

/* Print a header for the output */
void printHeader( void )
{
   int i; /* counter */

   printf( "\nSubscripts:\n" );

   /* output column head */
   for ( i = 0; i < SIZE; i++ ) {
      printf( "%3d ", i );
   } /* end for */

   printf( "\n" ); /* start new line of output */

   /* output line of - characters */
   for ( i = 1; i <= 4 * SIZE; i++ ) {
      printf( "-" );
   } /* end for */

   printf( "\n" ); /* start new line of output */
} /* end function printHeader */

/* Print one row of output showing the current
   part of the array being processed. */
void printRow( const int b[], int low, int mid, int high )
{
   int i; /* counter for iterating through array b */

   /* loop through entire array */
   for ( i = 0; i < SIZE; i++ ) {

      /* display spaces if outside current subarray range */
      if ( i < low || i > high ) {
         printf( "    " );
      } /* end if */ 
      else if ( i == mid ) { /* display middle element */
         printf( "%3d*", b[ i ] ); /* mark middle value */
      } /* end else if */
      else { /* display other elements in subarray */
         printf( "%3d ", b[ i ] );
      } /* end else */

   } /* end for */

   printf( "\n" ); /* start new line of output */
} /* end function printRow */




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