Rockwell-automation 2708-NBD VBASIC Language Development Kit Manual de usuario descargar pdf (Pagina 47)

A–B

Appendix

A–1

A-B VBASIC and Visual BASIC Tips

Misspellings

Don’t misspell names. BASIC is unforgiving of such errors since it will just

create a new variable which is zero or blank.

Strings in TYPEs

Strings which are defined in TYPE statements are of a fixed length. These

are always blank padded on the end.

Variables Beginning with “FN”

Do not start any variable name with FN, Fn, Fn, or fn. BASIC treats these as

a reference to the archaic DEF FN.... mechanism and produces a syntax error.

Accidental Omission of %, &, ! # OR $

If you leave the trailing character off of variable names, you will usually get

no warning from BASIC. Instead, the variable will be a different one than

what you expected. Watch out for this! If you happened to pick a

String/Integer mismatch, you will get syntax errors. Integer/Real mismatches

are very difficult to locate.

Another peculiarity of trailing characters is that if you have a function named

XYZ!, and you attempt to reference that function as XYZ# or XYZ% or

anything other than XYZ! or XYZ then you will get a MULTIPLE

DEFINITION error at the function declaration even though the reference is

many lines later.

Use of Colons as Statement Separators

Use of colon “:” as a statement separator can cause a number of problems

with both Visual BASIC and A-B VBASIC. An example follows:

CL2 : PRINT “This is a test” ;

1 2 ... 42 43 44 45 46 47 48 49 50 51 52 ... 83 84

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Rockwell-automation 2708-NBD VBASIC Language Development Kit Manual de usuario Pagina 47