This code helps to explain those two warnings seperately:

printf("%-2s", "\n");
printf("%s%s", "a");
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It prints:

Newline in left-justified string for printf at math1.pl line 1.

Use of uninitialized value in printf at math1.pl line 2.
 a
[download]

The OP already provided the document that explains the first warning. The warning, to be frank, is meaningless. They just feel worried that you are probably confusing yourself ;-)

The second warning was caused by the fact that we have two %s, which requires two strings, but only one is provided.