prog.10.10.c

// Dictionary lookup program

#include <stdio.h>

struct entry
{
	char word[15];
	char definition[50];
};

// Function to compare two character strings

int compareStrings (const char s1[], const char s2[])
{
	int i = 0, answer;

	while ( s1[i] == s2[i] && s1[i] != '\0' && s2[i] != '\0' )
		++i;

	if ( s1[i] < s2[i] )
		answer = -1;		/* s1 < s2 */
	else if ( s1[i] == s2[i] )
		answer = 0;			/* s1 == s2 */
	else
		answer = 1;			/* s1 > s2 */

	return answer;
}

// Function to look up a word inside a dictionary

int lookup (const struct entry dictionary[], const char search[],
			const int entries)
{
	int low = 0;
	int high = entries -1;
	int mid, result;
	int compareStrings (const char s1[], const char s2[]);

	while ( low <= high )
	{
		mid = (low + high) / 2;
		result = compareStrings (dictionary[mid].word, search);

		if ( result == -1 )
			low = mid + 1;
		else if ( result == 1 )
			high = mid - 1;
		else
			return mid;		/* found it */
	}

	return -1;				/* not found */
}

int main (void)
{
	const struct entry dictionary[100] =
	{
		{ "aardvark", "a burrowing African mammal"        },
		{ "abyss",    "a bottomless pit"                  },
		{ "acumen",   "mentally sharp; keen"              },
		{ "addle",    "to become confused"                },
		{ "aerie",    "a high nest"                       },
		{ "affix",    "to append; attach"                 },
		{ "agar",     "a jelly made from seaweed"         },
		{ "ahoy",     "a nautical call of greeting"       },
		{ "aigrette", "an ornamental cluster of feathers" },
		{ "ajar",     "partially opened"                  }
	};

	int		entries = 10;
	char	word[15];
	int		entry;

	int lookup (const struct entry dictionary[], const char search[],
			    const int entries);

	printf ("Enter word: ");
	scanf  ("%14s", word);

	entry = lookup (dictionary, word, entries);

	if ( entry != -1 )
		printf ("%s\n", dictionary[entry].definition);
	else
		printf ("Sorry, the word %s is not in my dictionary.\n", word);

	return 0;
}