Measuring string lenth in c

 #include<stdio.h>

int strlen(char *st){

char *ptr = st;

int len = 0;

while(*ptr!='\0'){

len++;

ptr++;

}

return len;

}

int main()

{

char st[] = "Harry";

int l = strlen(st);

printf("The lenth of this string is %d",l);

return 0;

}