在一个有序数组中查找具体的某个数字——二分法——函数法

（1）#include<string.h>
int main()
{
int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int left = 0;
int right = sizeof(arr) / sizeof(arr[0])-1;
int mid = 0;
int key = 11;
while (left <= right)
{
mid = (left + right) / 2;
if (arr[mid] > key)
{
right = mid - 1;
}
else if (arr[mid] < key)
{
left = mid + 1;
}
else
{
break;
}
}
if (left <= right)
{
printf("下标是%d\n", mid);
}
else
{
printf("找不到\n");
}

system("pause");
return 0;
}

（2）函数法
指针变量字节数

32位计算机——4个字节
64位计算机——8个字节
例：#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
int main()
{
char a = "c";
int b = 12;
short c = 10;
long d = 1;
double e = 1.0;
char *pa = &a;
int *pb = &b;
short *pc = &c;
long *pd = &d;
double *pe = &e;
printf("%d", sizeof(pa)); //4
printf("%d", sizeof(pb)); //4
printf("%d", sizeof(pc)); //4
printf("%d", sizeof(pd)); //4
printf("%d", sizeof(pe)); //4
system("pause");
return 0;
}

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
int binary_search(int arr[], int key, int temp)
{
int left = 0;
int right = temp - 1;

while (left <= right)
{
int mid = (left + right) / 2;
if (arr[mid] < key)
{
left = mid + 1;
}
else if (arr[mid]>key)
{
right = mid - 1;
}
else
{
return mid;
}
if (left > right)
{
return -1;
}
}
}
int main()
{
int key;
int arr[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
scanf("%d", &key);
int temp = sizeof(arr) / sizeof(arr[0]);    //数组的长度传不到函数
int res = binary_search(arr, key, temp);     //数组传参是首元素地址，需要在外面求得，传到函数里面
if (res == -1)
{
printf("找不到\n");
}
else
{
printf("找到了下标是%d", res);
}
system("pause");
return 0;
}

  如有错误，请指正