为什么输入1，编译器就炸了

#include <stdio.h>
#define NUM 10
int main()
{
    int a[NUM]={1,2,3,4,5,6,7,8,9,10};
    int left=0,right=NUM-1,mid,key;
    mid=(left+right)/2;
    printf("Enter kay:");
    scanf("%d",&key);
    while(left<right&&a[mid]!=key)
    {
        if(key<a[mid])
        right=mid-1;
        else if(key>a[mid])
        left=mid+1;
        mid=(left+right)/2;
    }
    if(a[mid]==key)
    printf("found");
    else
    printf("no found");
    return 0;
}

[此贴子已经被作者于2016-12-12 22:22编辑过]