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Statement Syntax |
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A valid program statement requires at least one directive. Depending on the directives used, various arguments and syntax elements may be needed to complete the statement. The example below illustrates the format of a typical program statement:
Example:
0010 Total: PRINT a,b,c+d ! Totals
Where:
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0010 |
Line Number (optional). Any integer between 1 and 64999. Each line number must be unique - the best practice is to assign line numbers in increments of 5 or 10 to allow for easy insertion of additional statements. When a line number precedes a statement, the statement will be included in the construction of a program. See Line Numbers. |
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Total: |
Line Label (optional). Descriptive name up to 127 characters long, followed by a colon. Alphanumeric line labels can be used in place of line numbers to identify statements within the program. |
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Directive. Keyword identifying the task to be performed. |
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a,b,c+d |
Arguments (optional). Data to be processed or system keywords that further define the directive. A space is required to separate the directive from its arguments. See Arguments below. |
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! Totals |
Comment (optional). Descriptive text beginning with an exclamation point ! or the keyword REM. Text following an exclamation point is ignored by the system; i.e. the exclamation point terminates a statement and passes execution to the next line of code. |
While some directives are executed without arguments, most accept/require data or keywords to perform their tasks. Argument components may be optional or mandatory - this depends on the directive and the task involved.
Most arguments supply some form of data for processing - a text or numeric value delivered in literal or variable form. See Data Types, Literals and Variables. Other types of arguments can redefine or augment the functionality of the directive itself - system parameters, mnemonics, options, and built-in keywords. See Primary Syntax Elements.
If more than one directive appears in a statement, it is considered a compound statement. Semi-colons ( ; ) are required to separate the different directives (and their arguments) until the end of the line:
0020 let x=a+b; print "Answer=",x; goto 1000
Each of the directives in a compound statement (between the semi-colons) would function the same if they were entered in sequence on separate lines.
A transfer of control into a compound statement starts processing from the first directive only. In the above example (statement 0020), it would be impossible to start processing at the PRINT or GOTO directive. However, it is possible to transfer control out of (and then back into) a compound statement if the directive is designed to return back to the current location (GOSUB / RETURN and FOR..NEXT):
0030 x=10;print x; gosub xyz; goto 1000
Directives that transfer control without returning (e.g., GOTO, EXITTO, RETURN) must appear at the end of a compound statement. The following is not valid because RETURN transfers control and the last statement is unreachable code:
print "hello"; return; if name$<>"" print "-", name$
Some directives cannot be included in a compound statement. See individual directives for any restrictions. For a list of all directives, see Directives in the PxPlus Language Reference.