search3.c

linux下的Ｃ语言开发

/********************************************************
 * search -- Search a set of numbers. 			*
 *							*
 * Usage:						*
 *	search						*
 *		You will be asked numbers to lookup	*
 *							*
 * Files:						*
 *	numbers.dat -- numbers 1 per line to search	*
 *			(Numbers must be ordered)	*
 ********************************************************/
#include <stdio.h>
#define MAX_NUMBERS	 1000	        /* Max numbers in file */
const char DATA_FILE[] = "numbers.dat";	/* File with numbers */

int data[MAX_NUMBERS];	/* Array of numbers to search */
int max_count;		/* Number of valid elements in data */
int main()
{
    FILE *in_file;	/* Input file */
    int	middle;		/* Middle of our search range */
    int low, high;	/* Upper/lower bound */
    int search;		/* number to search for */
    char line[80];	/* Input line */

    in_file = fopen(DATA_FILE, "r");
    if (in_file == NULL) {
	fprintf(stderr,"Error:Unable to open %s\n", DATA_FILE);
	exit (8);
    }

    /*
     * Read in data 
     */

    max_count = 0;
    while (1) {
	if (fgets(line, sizeof(line),  in_file) == NULL)
	    break;

	/* convert number */
	sscanf(line, "%d", &data[max_count]);
	++max_count;
    }

    while (1) {
	printf("Enter number to search for or -1 to quit:" );
	fgets(line, sizeof(line), stdin);
	sscanf(line, "%d", &search);

	if (search == -1)
	    break;

	low = 0;
	high = max_count;

	while (1) {
	    middle = (low + high) / 2;

	    if (data[middle] == search) {
		printf("Found at index %d\n", middle);
		break;
	    }

	    if (low == high) {
		printf("Not found\n");
		break;
	    }

	    if (data[middle] < search)
		low = middle;
	    else
		high = middle;
	}
   }
   return (0);
}