C语言作业（二）

1.在数组中查找某个数字

#include <stdio.h>

int main()
{
    int arr[] = { 1,2,3,4,5,6,8,9,10,11 };
    int k = 7;
    int sz = sizeof(arr) / sizeof(arr[0]);//求解数组的元素个数
    int left = 0;
    int right = sz - 1;
    while (left <= right)
    {
        int mid = (left + right) / 2;
        if (arr[mid] > k)
        {
            right = mid - 1;
        }
        else if (arr[mid] < k)
        {
            left = mid + 1;
        }
        else
        {
            printf("找到了，下标是：%d\n", mid);
            break;
        }
    }
    if (left > right)
    {
        printf("找不到\n");
    }
    return 0;
}

2.使用递归打印1234

#include <stdio.h>

void print(int n)
{
    if (n > 9)
    {
        print(n / 10);
    }
    printf("%d", n % 10);
}
int main()
{
    int num = 1234;
    print(num);
    return 0;
}

3.模拟strlen(法一)

#include <stdio.h>
#include <string.h>
int my_strlen(char* str)
{
    int count = 0;
    while(*str !='\0')//指针从左往右，直到遇到/0停下
    {
        count++;
        str++;
    }
    return count;
}
int main()
{
    char arr[] = "jingying";
    int len = my_strlen(arr);
    printf("len = %d\n", len);
    return 0;
}

4.模拟strlen(法二:递归法)

#include <stdio.h>
#include <string.h>
int my_strlen(char* str)
{
    if (*str != '\0')
        return 1 + my_strlen(str + 1);//指针向右移动1，字节数+1
    else
        return 0;
}
int main()
{
    char arr[] = "jingying";
    int len = my_strlen(arr);
    printf("len = %d\n", len);
    return 0;
}