How to determine number of electrons lost or gained?

A neutrally charged atom, or a normal atom, has the same number of protons as electrons. An atom of Carbon, C, has 6 electrons and protons. If the atom gains or looses an electron(s), the atom will become an ion. To figure out how many electrons were lost/gained, you can do one of two things: look at the charge of the ion; or look at the difference in the amount electrons and protons. Say you have two element symbols: C and C-2. The ion, C-2, would have gained two electrons. If it were C+2, it would have lost two electrons. If you only have the number of electrons, you simply look at the difference to the number of protons. Ex: 
Element 1- Protons:12 Electrons:13
This atom has gained an electron, giving it a -1 charge.