I want to create console applications for linux and I was wondering if there is any standard for the output of applications?
Should I follow some guidelines, or can I do whatever I want?
If there is a standard, does anyone know if there is a library I can use to output properly? I;m programming in C++.
Almost all (Linux) command line utilities follow the posix guidelines, although this is mostly about command line parameters and not so much output.
I recommend to follow most of the GNU coding standards. In particular, from a naive user's point of view, I really like the --help and --version options (which are sadly not mandated by Posix). You may want to use, for parsing of program arguments, the argp functions provided by GNU Libc.
You may want to use ncurses for full-screen console input & output, or GNU readline to read an editable line of input. See also this and this answers.
I also suggest you to make your console applications free software (e.g. GPL licensed) and publish them on some versioned repository like github or gitorious etc etc...