strlen() implementation in c

str_len_arr.c

#include <stddef.h>
/**
 * return length of valid string which has '\0' or 0 as terminated
 */
size_t
str_len( const char *str)
{
    size_t i;
    for( i = 0; str[i] != '\0'; i++);
    return i;
}

str_len_ptr.c

#include <stddef.h>
/**
 * return length of valid string which has '\0' or 0 as terminated
 */
size_t
str_len( const char *str)
{
    const char *p = str;
    // while(*p != '\0') <=> while(*p != 0) <=> while(*p) 
    for(p = str; *p; p++);
    return (p - str);
}