mistake in String Functions: The string.h Library

Question

at the code in second slide of String Functions(""The string.h Library""), there is this line:
printf("Length of s1 is %d\n", strlen(s1));
it's a mistake, becouse strlen gives size_t ( unsigned long ), so you need this:
printf("Length of s1 is %ld\n", strlen(s1));
(%ld insted of %l) to work properly