There is supposed to be an even number, unless you have a special half link*.
Two half inch links that are different to each other make a pair. You need an even number to join them up. See pic below.
*note A half link looks like one of these: (Which you won't have).
Remove the chain and measure it: 120 links = 60"; 118 = 59"
You may be asking because it's time to get a new chain, therefore your chain will measure slightly more than an exact number of inches. But not so much as to confuse 118 vs 120.