SAS Constants
You may have noticed that TYPE was defined to be a single byte character-the compiler first saw it in the first INPUT statement using an informat. Since TYPE is a character variable, it makes sense that the constant in the IF statement is a character constant.
INPUT @20 TYPE $1. @; IF TYPE = '1' THEN
A character constant is anything enclosed in a matching pair of quotes (either single or double).
A numeric constant is a number not enclosed in quotes.