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80 lines
1.9 KiB
Markdown
80 lines
1.9 KiB
Markdown
[GOSUB](GOSUB) sends the program flow to a sub procedure identified by a line number or label.
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## Syntax
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> GOSUB {lineNumber|label}
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## Description
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* Use [RETURN](RETURN) in a sub procedure to return to the next line of code after the original [GOSUB](GOSUB) call. [END](END) or [SYSTEM](SYSTEM) can also be used to end program.
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* GOSUB and GOTO can be used **within** [SUB](SUB) or [FUNCTION](FUNCTION) procedures, but cannot refer to a label located outside the procedure.
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## QBasic
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* Too many GOSUBs without a [RETURN](RETURN) can eventually cause "Out of Stack Errors" in QBasic as each GOSUB uses memory to store the location to return to. Each [RETURN](RETURN) frees the memory of the GOSUB it returns to.
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## Example(s)
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Simple usage of GOSUB
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```vb
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PRINT "1. It goes to the subroutine."
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GOSUB subroutine
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PRINT "3. And it returns."
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END
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subroutine:
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PRINT "2. It is at the subroutine."
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RETURN
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```
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```text
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1. It goes to the subroutine.
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2. It is at the subroutine.
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3. And it returns.
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```
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What happens if two GOSUB executes then two RETURN's?
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```vb
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start:
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a = a + 1
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IF a = 1 THEN GOSUB here: PRINT "It returned to IF a = 1": END
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IF a = 2 THEN GOSUB there: PRINT "It returned to IF a = 2": RETURN
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here:
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PRINT "It went here."
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GOTO start
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there:
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PRINT "It went there."
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RETURN
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```
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```text
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It went here.
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It went there.
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It returned to IF a = 2
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It returned to IF a = 1
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```
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*Explanation:* When a = 1 it uses GOSUB to go to "here:", then it uses GOTO to go back to "start:". a is increased by one so when a = 2 it uses GOSUB to go to "there:", and uses RETURN to go the last GOSUB (which is on the IF a = 2 line), it then encounters another RETURN which makes it return to the first GOSUB call we used on the IF a = 1 line.
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## See Also
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* [ON...GOSUB](ON...GOSUB)
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* [ON...GOTO](ON...GOTO), [GOTO](GOTO)
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* [ON ERROR](ON-ERROR), [RESUME](RESUME)
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* [ON TIMER (n)](ON-TIMER-(n))
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* [Line number](Line-number)
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