C語言 - Binary Search 使用迴圈

1. 一組已排序n個整數
2. left = 0, right = n - 1
3. middle = (left + right) / 2
4.
searchnum > list[middle], left = middle + 1
searchnum = list[middle], return middle
searchnum < list[middle], right = middle - 1

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

int binsearch(int list[], int searchnum, int left, int right);

int main(int argc, char *argv[])
{
    int searchnum, left, right, pos;
    int list[] = {11, 22, 33, 44, 55, 66, 77, 88, 99};

    printf("Enter the numbfer you want to search: ");
    scanf("%d", &searchnum);

    left = 0;
    right = (sizeof(list)/sizeof(list[0])) - 1;
    pos = binsearch(list, searchnum, left, right);
    if (pos == -1)
        printf("not found\n");
    else
        printf("found pos: %d\n", pos);

    return 0;
}

#define COMPARE(x, y) (((x) < (y)) ? -1 : ((x) == (y)) ? 0 : 1)
int binsearch(int list[], int searchnum, int left, int right)
{
    int middle;
    while (left <= right) {
        middle = (left + right) / 2;
        switch (COMPARE(list[middle], searchnum)) {
        case -1:
                left = middle + 1;
                break;
        case 0:
                return middle;
        case 1:
                right = middle - 1;
                break;
        }
    }
    return -1;
}