How can I write my own strlen function in c.

#include<stdio.h>
int my_strlen(char *str)
{

	int rv;
	
	
	for (rv=0; str[rv] != 0; rv++) 
        {
       
         }
	return rv;
}
int main(int argc, char const *argv[])
{
	char str[10]={'H','e','l','l','o','\0'};
	printf("\nLength is %d\n",my_strlen(str));
	return 0;
}