FORTRAN

FORTRAN (or ForTran or Fortran) is a computer programming language developed by IBM in the 1950s with a focus on scientific and engineering applications. FORTRAN is still in use today in the sciences despite the dominance of C++ (http://planetmath.org/C) for most general applications and Mathematica and Maple for algebra applications. Sloane’s On-Line Encyclopedia of Integer Sequences does not include FORTRAN source code but provides links to it. The current version is FORTRAN 2003; an international group of corporations and programmers is working on FORTRAN 2008.

The following FORTRAN program takes two integers as inputs and outputs their greatest common divisor using Euclid’s algorithm. It requires positive integers as inputs. NB is just a variable name that has nothing to do with Zentrums. The function NGCD is defined after the main program. It was written by Wikipedia user Rwwww:

*     euclid.f (FORTRAN 77)*     Find greatest common divisor using the Euclidean algorithm*     Written by: Wikipedia User:Rwwww      PROGRAM EUCLID        PRINT *, 'A?'        READ *, NA        IF (NA.LE.0) THEN          PRINT *, 'A must be a positive integer.'          STOP        END IF        PRINT *, 'B?'        READ *, NB        IF (NB.LE.0) THEN          PRINT *, 'B must be a positive integer.'          STOP        END IF        PRINT *, 'The GCD of', NA, ' and', NB, ' is', NGCD(NA, NB), '.'        STOP      END      FUNCTION NGCD(NA, NB)        IA = NA        IB = NB    1   IF (IB.NE.0) THEN          ITEMP = IA          IA = IB          IB = MOD(ITEMP, IB)          GOTO 1        END IF        NGCD = IA        RETURN      END