Apple IIe - Page 137

Apple BASIC Reference Guide 137
In effect, a GOSUB or ON/GOSUB statement is converted to a
GOTO or ON/GOTO statement when POP is executed. The
program "forgets" that it is in a subroutine. As a result, when a
POP statement
is executed, the next RETURN statement branches
the program control to the line after the GOSUB statement
before the previous GOSUB statement. In other words, the
program "forgets" where the subroutine was called from, so it
returns to a previous GOSUB statement.
A POP
statement is used, in general, to exit a subroutine.
10 x = 5
20 y = 10
Example
30 GOSUB 100
40 END
100 PRINT X
110
IF X > 0 THEN POP:GOTO 130
120 RETURN
130
PRINTY
140 END
]RUN [Ret]
5
10
The previous example contains a program that uses a POP
statement to exit a subroutine . At line 10, Xis assigned the value
5. At line 20, Y is assigned the value 10. At line 30, the subroutine
at line 100 is called.
At line 100, the value of Xis displayed. Line 110 is an IF/THEN
statement that tests the condition X > 0. Since the value of X is
greater than zero , the condition is true. As a result, the POP
statement is executed, and the program control branches to line
130. At line 130, the value of Y is displayed.