The arithmetic IF statement has been for several decades a three-way arithmetic conditional statement, starting from the very early version (1957) of Fortran, and including FORTRAN IV, FORTRAN 66 and FORTRAN 77. Instead of the common if statements seen in other languages, the statement defines three different branches depending on whether the result of an expression was negative, zero, or positive, in said order, written as:
IF (expression) negative,zero,positive
While it was originally the only kind of IF statement provided in the language, the feature became more and more unused after the introduction of the more powerful and common logical IF statement, so that it was finally labeled obsolescent in Fortran 90 .
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