Editing Line number (section)

=== BASIC ===
Introduced in 1964, [[Dartmouth BASIC]] adopted mandatory line numbers, as in JOSS, but made them integers, as in FORTRAN. As defined initially, BASIC only used line numbers for {{code|GOTO}} and {{code|GOSUB}} (go to subroutine, then return). Some [[Tiny BASIC]] implementations supported numeric expressions instead of constants, while [[switch statement]]s were present in different dialects ({{code|ON}} {{code|GOTO}}; {{code|ON}} {{code|GOSUB}}; {{code|ON ERROR GOTO}}).

Line numbers were rarely used elsewhere. One exception was allowing the pointer used by {{code|READ}} (which iterated through {{code|DATA}} statements) to be set to a specific line number using {{code|RESTORE}}.

<syntaxhighlight lang="bbcbasic">
  1 REM RESTORE COULD BE USED IF A BASIC LACKED STRING ARRAYS
  2 DIM M$(9): REM DEFINE LENGTH OF 9 CHARACTERS
  5 INPUT "MONTH #?"; M: IF M<1 OR M>12 THEN 5
  7 RESTORE 10*M: READ M$: PRINT M$
 10 DATA "JANUARY"
 20 DATA "FEBRUARY"
 30 DATA "MARCH"
 ...
</syntaxhighlight>

In the first editions of Dartmouth BASIC, {{code|THEN}} could only be followed by a line number (for an ''implied GOTO''), not - as in later implementations - by a statement.

The range of valid line numbers varied widely from implementation to implementation, depending on the representation used to store the binary equivalent of the line number (one or two bytes; signed or unsigned). While Dartmouth BASIC supported 1 to 99999, the typical microcomputer implementation supported 1 to 32767 (a signed 16-bit word).

{| class="wikitable"
|+ Valid Line Numbers in [[Tiny BASIC#Dialects compared|Early BASIC Implementations]]
|-
! Range !! Dialect
|-
| 1 to 254 || MINOL
|-
| 1 to 255 || Tiny BASIC Design Note
|-
| 2 to 255 || Denver Tiny BASIC
|-
| 0 to 999 || UIUC BASIC
|-
| 1 to 2045 || [[BASIC-PLUS|DEC BASIC-8]]
|-
| 0 to 32767 || LLL BASIC, NIBL
|-
| 1 to 32767 || [[Integer BASIC|Apple I BASIC]], [[Level I BASIC]], [[Palo Alto Tiny BASIC]]
|-
| 0 to 65529 || [[GW-BASIC]], [[IBM BASIC]]
|-
| 1 to 65535 || [[Altair BASIC|Altair 4K BASIC]], MICRO BASIC 1.3, 6800 Tiny BASIC, Tiny BASIC Extended
|-
| 1 to 99999 || [[Dartmouth BASIC]]
|-
| 1 to 999999 || [[SCELBAL]]
|-
| 0 to 1*10^40-1 || [[QBASIC]] 1)
|}
1) While QBASIC does make use of structured programming and thus doesn't need line numbers, it is still possible to run code with line numbers in QBASIC.