Mark Wickens

ON GOSUB

Purpose

Jumps to a specified subroutine in accordance with a specified branching condition.

Format

ON     condition       GOSUB   [ branch          [, [ branch
       └───┬───┘                destination ]       destination ] ]*
   Numeric expression

```basic
                    ⎧  destination branch line number  ⎫
                    ⎪  └─────────────┬──────────────┘  ⎪
                    ⎪           Line number            ⎪
Branch destination: ⎨                                  ⎬
                    ⎪  # program area number           ⎪
                    ⎪    └────────┬────────┘           ⎪
                    ⎩    Single character; 0~9         ⎭

Example

ON A GOSUB 1000, 1100, 1200

Parameters

1. branch condition: Numeric expression truncated to an integer
2. line number: Integer in the range of 1 ≦ line number ≦ 65535
3. program area number: Singe character, 0~9

Explanation

1. The GOSUB statement is executed in accordance with the value of the expression used for the branch condition. For example, execution jumps to the first branch destination specified when the value is 1, to the second destination when the value is 2, etc.
2. Program execution does not branch and execution proceeds to the next statement when the value of the branch condition is less than 1, or if a branch destination corresponding to that value does not exist.
3. Up to 99 branch destinations may be specified.

Sample Program

10  S1=0: S2=0
20  FOR I=1 TO 100
30  ON (I MOD 2)+1 GOSUB 1000, 1100
40  NEXT I
50  PRINT "S1="; S1
60  PRINT "S2="; S2
70  END
1000 S1=S1+I: RETURN
1100 S2=S2+I: RETURN

S1 calculates sum of even numbers from 1 to 100, S2 calculates sum of odd numbers from 1 to 100.