折中查找（二分查找）

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#include <stdio.h>
#define n 10
int main()
{
    int left = 0;
    int right = n-1;
    int a[n];
    int i, mid, key;//key 是要查找的数字；mid 表示中间值
    printf("input the key number\n");
    scanf("%d",&key);
    printf("input ten number\n");
    for(i =0; i < n; i++)
    {
        scanf("%d",&a[i]);
    }
    while(left <= right)
    {
        mid = (left + right)/2;
        if(key == a[mid])
        {
            break;
        }
        else if(key > a[mid])
            left = mid + 1;//要找的数可能在中上，右值不变，左值移到中间再 + 1
        else
            right = mid - 1;//要找的数可能在中下,左值不变，右值移到中间再 - 1
    }
    if(left > right)//不在区间内
    {
        printf("it is not find the key\n");
        return -1;
    }
    else
    {
        printf("mid =%d\n", mid);
    }
    return 0;
}