1:实现strlen

  4 int main(int argc, const char *argv[])
  5 {
  6     char s[30] = "hello world";
  7     int i = 0;
  8 
  9     while(s[i]!='\0')
 10     {
 11         i++;
 12     }
 13     printf("len = %d\n", i);
 14     return 0;
 15 } 

运行结果：

2：实现strcpy

 16     char s1[32] = "hello world";
 17     char s2[32] = "hqyj";
 18     printf("s1 = %s\n", s1);//hello world
 19     printf("s2 = %s\n", s2);//hqyj
 20     int i = 0;
 21     while(s2[i] != '\0'){
 22         s1[i] = s2[i];
 23         i++;
 24     }
 25     //将 s2 的  '\0' 也复制给s1
 26     s1[i] = s2[i];
 27 
 28     printf("s1 = %s\n", s1);//hqyj
 29     printf("s2 = %s\n", s2);//hqyj
 30     return 0;
 31 }

运行代码：