How the following C program works?

[itiger]

# include <stdio.h>
void main()
{
   char str[] = "Zingle Bell Zingle Bell";
   printf("%.#s %.2s", str, str);
}

output:
#s Zi

(how the '%s' type specifier works in this case.)

[whodgson]

I cannot find any reference meaning for %.#s or why fprint would output #s which may be printed as a result of undefined behavior. %.2s is applying two places of precision to string str and so prints Zi bearing in mind that a character is treated like an int.