Fortran Programming Interview Questions and Answers

1 :: Do spaces mater in Fortran equations?

No. Spaces are generally added for clarity. Some compilers get upset if you write things like " INTEGERI,J" rather than INTEGER I,J". Simple neatness will keep you out of these problems. Remember that a space is required in column 6 if you aren't continuing from the previous line. The following are all equivalent:

x=x*y**2*sin(x)
x=x * y**2 * sin(x)
x = x * y ** 2 * sin ( x )

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2 :: What is the advantage of an array over a spreadsheet format?

Both can store similar types of information in a neatly labeled and organized way. The advantage lies in where they are used. You have more control over how Fortran arrays are used than how the contents of aspreadsheet are used. In addition for any given operation on an array of numbers, once the Fortran is written, it will do the job much faster than aspreadsheet. On the other hand, when operations are not complex and computer execution time is not a problem using the spreadsheet is probably your best bet.

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3 :: What can we do if our lines wrap around to the next line?

You have to get a feel for the location of the 72nd character position on the screen, or do a lot of counting. Once you hit column 72, you must hit the RETURN key, put some character (I like & or #) in column 6 of the next line then pick up typing where you left off. I usually stop before column 72 at some natural break point between variables:

123456789012345678901234567890123456789012345678901234567890123456789012
IF ( (X.LT.2.0.AND.Y.GT.30.0).OR.(X.GT.1000.0.AND.Y.LT.-40.))
& PRINT *,' CALCULATION IS IN TROUBLE'

Since Fortran tends to ignore blanks, the extra ones in the above 2 lines don't cause problems.

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4 :: Why does not Fortran have intrinsic functions for something as simple as factorial?

Two reasons. Factorial isn't all that common in heavy duty scientific and engineering applications. When it does occur, it almost always in a context where it is more computationally efficient to generate it as you go. You need 2! first then 3!, then 4!, etc. You are basically stuck doing a factorial within the context of a do loop unless you get really good and learn to write "recursive functions", but then you are just fooling yourself and writing another form of do loop. When you are taking the factorial of a large number and don't need an exact answer you can resort to Stirling's Approximation. A Fortran statement that will load the value of this approximation into the variable nfact is.

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5 :: How do we know where various steps go in a Fortran program?

Some commands have special locations, but most are located by the needs of the specific program. The PROGRAM card is always first. Statements giving variable types (INTEGER, REAL, LOGICAL, CHARACTER, ...) should precede "executable" statements. The END card must always be at the end of the program unit.

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