1.数组

#include<stdio.h>
int Strlen(char* str)
{
	int count = 0;
	while (*str != '\0')
	{
		count++;
		str++;
	}
	return count;
}
int main()
{
	int len = Strlen("abcdef");
	printf("%d\n", len);
	return 0;
}

2.递归

#include<stdio.h>
int Strlen(char* str)
{
	if (*str != '\0')
		return 1 + Strlen(str + 1);
	else
		return 0;
}
int main()
{
	int len = Strlen("abcdef");
	printf("%d\n", len);
	return 0;
}

3.指针-指针

#include<stdio.h>
int Strlen(char* str)
{
	char* start = str;
	while (*str != '\0')
	{
		str++;
	}
	return (str-start);
}
int main()
{
	int len = Strlen("abcdef");
	printf("%d\n", len);
	return 0;
}