Arithmetic IF is a kind of conditional command used in some programming languages such as FortranLanguage, FocalLanguage?, and TeXnicard. It is considered a old (obsoleted) feature of FORTRAN. It means a conditional based on whether a number is being negative/zero/positive.
Some programming languages may use a imperative arithmetic IF, which takes line numbers (or line labels) to jump to based on the result being negative/zero/positive.
Some use functional arithmetic IF, where it takes the number to check and the three responses to give, one if negative, one if zero, one if positive; rather than causing flow control or side effects.
I happen to think that DeeCee would be better if it used arithmetic IF rather than how it actually uses.