# on...gosub statement

The on... gosub statement transfers
control to a local subroutine designated by a specific statement label
according to the positional value returned by the expression. The
syntax can also be specified as on...go sub...(allowing
a space between go and sub).

## Syntax

```
on exp gosub statement.label{,
 statement.label...}

on exp gosub statement.label,...,
 statement.label,
 statement.label
```

## Parameter(s)

| exp | Numeric value that corresponds to the position of comma-separated statement.labels. |
| --- | --- |

## Description

If required, the *exp* is truncated to an integer. The program executes the local subroutine
at the *statement.label* that corresponds to *exp*. For example, if the expression evaluates to 1, the
first subroutine is executed. If the *exp* evaluates
to a number less than 1, or to a number greater than the number of
statement labels, no action is taken. Execution continues at the first
executable statement following the on...gosub.

The local subroutine must be terminated with a return statement. At the end of the subroutine, the program returns to
the statement following the on...gosub statement.

For ease of reading, the on...gosub *statement.label* list can be spread over multiple lines
if each continued line is terminated with a , (comma).

## Example(s)

If response is 1, this branches
to subroutine 8000. If it is 2, it branches to subroutine 9000. If
it is 3, it branches to subroutine 9500.

```
loop
print ’1) doit 2) printit 3) deleteit’
input response
until num(response) do repeat
if response >=1 and response <= 3 then
on response gosub 8000,9000,9500
end
```
In this example, the result of the `index()` function is used as the index expression to determine which subroutine
is called. If the response is `a`, then subroutine `doit` is called, and so on.

```
print ’a) doit b) printit c) deleteit’
input response,1
on index(’abc’,response,1) gosub doit,printit,deleteit
```
When the value of the index expression has a large number
of possible branches, readability is improved by using the multiple
line syntax.

```
on response gosub 10,20,30,40,50,60,
70,80,90,100,110,120,130
```

## See also

- [on...goto statement](https://d3codex.com/pickbasic-flashbasic/on-goto-statement/)
- [return statement](https://d3codex.com/pickbasic-flashbasic/return-statement/)
- [statement labels](https://d3codex.com/pickbasic-flashbasic/statement-labels/)
- [Statements and functions](https://d3codex.com/pickbasic-flashbasic/statements-and-functions/)

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Source: https://d3codex.com/pickbasic-flashbasic/on-gosub-statement/ - part of the D3Codex reference.