Line number
In computing, a line number is a sequential numerical identifier assigned to a particular line of text within a file or program source code, serving as a reference for editing, navigation, and error reporting.[1] This concept is central to text file organization, where the POSIX standard defines a line as a sequence of zero or more non-newline characters plus a terminating newline character, with line numbers denoting the ordinal position of each such unit in the file.[2] In programming contexts, line numbers originated in the mid-20th century to address limitations of early input methods like punched cards and teletypes, providing a simple way to order and modify code without full-screen editors.[3] The Dartmouth BASIC language, introduced in 1964, exemplifies this usage by requiring every program statement to begin with a unique integer line number, typically in increments like 10 to allow for easy insertions.[4] These numbers determined execution order, as the system automatically sorted lines numerically upon entry, and supported control structures such as GOTO for branching to a specified line or GOSUB for subroutine calls.[4] Editing was streamlined: retyping a line with an existing number replaced it, entering a number alone deleted the line, and new lines were inserted based on their numerical value relative to others.[4] Similar conventions appeared in other early languages, such as FORTRAN for specifying loops and input formats, though they were not always mandatory.[3] While modern programming paradigms favor labels, indentation, and structured control flow over explicit line numbers, the practice endures in legacy systems, compiler directives like C's #line for adjusting error message contexts, and debugging outputs that reference line positions.[1] In contemporary tools, such as integrated development environments (IDEs), line numbers are optionally displayed alongside code to facilitate quick location of statements during development and troubleshooting.[5] For instance, Visual Studio enables line number visibility through its options menu, enhancing productivity for large codebases.[5] Overall, line numbers bridge historical computing constraints with ongoing needs for precise textual addressing across documents and software.Overview and Purpose
Definition
In computing, line numbers are integer labels prefixed to individual lines of source code in certain early interpreted programming languages, such as BASIC, serving as unique identifiers for each statement within a program. These numbers typically begin at 1 (or often 10 in practice to allow for insertions) and increment sequentially, with the interpreter or compiler sorting and executing the lines in numerical order regardless of input sequence. This structure ensures programs are organized and executable as a cohesive unit.[6][7] Line numbers differ from other numbering systems in programming, such as memory addresses that denote runtime locations in RAM or statement labels in assembly languages that function solely as optional references for branching. Instead, line numbers are a mandatory syntactic element in languages like BASIC, integral to the program's structure and parsing. For instance, in BASIC, a simple statement might appear as10 PRINT "HELLO", where 10 is the line number followed by the command to output text.[6]