ON...GOTO... allows conditional jumping.
ON expression GOTO line number 1, line number 2, ....line number n.
10 ON A GOTO100,200,300 20 END
If A=1 then the program will go to line 100
If A=2 then the program will go to line 200
If A=3 then the program will go to line 300
If A=1.3 then the program will go to line 100.
ON GOTO will cause program execution to jump to a line number chosen from the list of line numbers positioned immediately after GOTO. The selection of a particular line number in this list is determined by the value of [expression].
The line numbers may themselves be expressions.
The value of [expression], in the above example A, is truncated to an integer.
It must be noted that the value is truncated to an integer and NOT rounded up. So if the above example A=1.9 then the program will go to line 100.
If the value of [expression] is zero or greater than number the of line numbers in the list, then program execution Will continue with the next statement.
In the above example, if A=4, or A=0 then the program will automatically go to line 20, and the END will be executed.
The maximum value of [expression] allowed is 255.
If the value of [expression] is greater than 255 then a ’Magnitude Error' will occur and program execution will stop. If in the above example A=256 then an error will occur. A 'Magnitude Error' will also occur if the value of [expression] is negative.
10 ON A GOTO 100,200,300: PRINT "HELLO" 20 END
If A>3 or A=0 then the program will not go to any of the lines but will immediately print "Hello", and then END will be executed.