二分查找

基本思想：先选取中间位置的数字，与要查找的key值比较，若相等，则查找成功；若大于key值，则key值位于前半部分；否则位于后半部分，一步步折半查找。代码如下：

#include<stdio.h>void binary_search(int key, int a[], int n) {int low, high, mid, count=0,count1=0;low=0;high=n-1;while(low<high) {count++;mid=(low+high)/2;if(key>a[mid]) {low=mid+1;} else if(key<a[mid]) {high=mid-1;}else if(key==a[mid]){printf("查找成功！\n查找%d次!\n a[%d]=%d",count,mid,key);count1++;break;}}if(count1==0) {printf("查找失败！\n");}}int main() {int n,i,key;int *a=(int *)malloc(n*sizeof(int));printf("请输入数组的长度：\n");scanf("%d",&n);printf("请输入数组元素：\n");for(i=0;i<n;i++) {scanf("%d",&a[i]);}printf("请输入要查找的元素：\n");scanf("%d",&key);binary_search(key,a,n);printf("\n");free(a);return 0;}