Declaring variables

Should one declare variables (in C) at the begining of a function? I allways declared them before the first use, now i start to question if this is right.
What is the right thing to do /prog/?

This "she" and "her" shit in Computer Science has to fucking stop.

It's like talking about, um, the beauty industry (or whatever) and constantly saying "he" or "him" when talking about make-up or some other crap.