What header file should I use?

When I write a piece of code in C i often ask myself what library should I use. Stdio or iostream? I will like to know your opinion releated with this problem or I will like to find out other libraries for reading from the keyboard and writing on the screen.

Read the documentation for the functions you use and it should tell you which headers are required.

Seriously, if you're using C "open()" IO, stick to that. If you're using stdio "fopen()", stick to that (more portable anyway).

If you're using C++ and want to use *any* C++ IO, stick to that (cin, cout etc)

If you use a library like curses, use that exclusively.

Basically, don't mix & match, it will only cause tears down the line, particularly cross platform.

that depends what you want to do, for righting text and organizing it i would suggest stdio, but using actual file io use iostream..

you may have problems using iostream with c because its for c++,

funny though, i never tried including iostream in a c project, i just assumed it wouldn't work.

http://www.digitalmars.com check out their runtime library reference.

It comes down to 1 thing, what language are you using?
If you are using C, use stdio and scanf(), printf(), fprintf(), etc. That is a C library and uses C functions.
If you are using C++, use iostream with cin, cout, etc... and fstream with istream, ostream, ... These are C++ libraries that use C++ classes.
Good luck!