Using Secure Printf

Question

My programming book is saying that when I am using printf, I should use like these:
printf("%s","Why like this");
printf("Why not like this");
Why should I use with format-control string?

Answer 1

I found the answer in internet. If I use printf without format-control string, the user can enter some arguments that can effect my program. For example:%n. Thanks to everybody.

Answer 2

I have just read that link. :D

Answer 3

Could you also answer my 2d array question? @Ace