Rockwell-automation 2708-NBD VBASIC Language Development Kit Manual de usuario descargar pdf (Pagina 48)

Appendix A

A-B VBASIC and Visual BASIC Tips

A–2

The programmer assumed that this statement would clear the second line of

the display and then print “This is a test”. But, this is not what actually

happens! This is compiled as:

CL2 : PRINT “This is a test” ;

where CL2 is a local label which is effectively ignored.

The rule should be NEVER have a line which looks like:

< identifier > : < rest of line >

unless you INTEND for <identifier> to be a label.

CONSTant Declarations

“CONST name = value” does not quite follow the same rules as variable

assignments in the same position. The major difference is that the type of

‘name’ is determined by the contents of ‘value’. A DEFINT or DEFSNG #,

or $ after the name to set the type explicitly. The trailing symbol is NOT

required when the constant is referenced.

PRINT “text”; : <statement>

A problem for Pascal and C programmers is coding: PRINT “text”,

<statement> instead of: PRINT “text”; : <statement>

If the statement is a function such as “e = ReadStr%(3,s$)” then the result is

for e to retain its previous value, and for an extra 0 or 1 to follow the printed

text.

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 83 84

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Rockwell-automation 2708-NBD VBASIC Language Development Kit Manual de usuario Pagina 48