ON ... GOTO

ON … GOTO

Syntax

ON <expression> GOTO <label0>, <label1>, <label2>, ..., <labelN>
ON <expression> GO TO <label0>, <label1>, <label2>, ..., <labelN>

Transfers control to one of a series of specified line numbers or labels based on the value of an expression.

Parameters

<expression>: An integer expression that determines which label to jump to. It can be any numeric expression.
<label0>, <label1>, <label2>, ..., <labelN>: A comma-separated list of line numbers or labels. These are the destinations for control transfer based on the value of <expression>.

The value of expression is converted to a uByte (Unsigned Byte), so, for example, a value of 256 will be converted to 0. If the expression value is greater than the number of labels, this instruction will be ignored and the execution will continue normally.

This sentence uses a jump table for faster execution.

Example with ON … GOTO

 5 REM Random value between [0..3] both included
10 LET X = INT(RND * 4)
20 ON X GOTO 50, 100, 150
30 PRINT "Invalid choice: "; X
40 GOTO 10
50 PRINT "You chose option 0"
60 END
100 PRINT "You chose option 1"
110 END
150 PRINT "You chose option 2"
160 END

In this example,

if X is 0, the execution will jump to line 50
if X is 1, it will jump to line 100;
if X is 2, it will jump to line 150.
If X is outside this range, the ON ... GOTO sentence will be ignored.
The program will print “Invalid choice” and ask for input again.

Remarks

The <expression> is evaluated, and if it results in a value outside the range 0 to N (where N is the number of labels), no action is taken.
ON ... GOTO is a structured programming alternative to multiple IF...THEN...GOTO statements.

Compatibility

This statement is not compatible Sinclair BASIC.