Code 128C encodes only numbers containing an even number of characters. Since the numbers are "interleaved" into pairs, with two numbers encoded into every barcode character, a very high-density barcode is created. If the number that is to be encoded does not contain an even number of characters, a leading zero will be added.
Code 128C includes a set of 100 numeric data character pairs from 00 through 99 inclusive, and also includes special characters. This enables double-density numeric digits (two digits per bar coded character) to be encoded. Data encoded in a Code 128C must contain an even number of characters. If the data contains an odd number of characters, a zero (0) will be inserted at the beginning of the bar code.