what is the library needed for functions

I'm learning C++ from a slightly outdated book when I tried using functions it gave me a few weird errors. I'm sure I'm missing a library. please help thanks in advance!

these are the librarys I'm using:
iostream
stdlib.h
cmath
You need to post the errors. We cannot read minds.

BTW, in C++, stdlib.h changed to cstdlib (no extension, just like cmath used to be math.h).
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