Line number

In computing, a line number is a method used to specify a particular sequence of characters in a . The most common method of assigning numbers to lines is to assign every a unique number, starting at 1 for the first line, and incrementing by 1 for each successive line. In the C programming language the line number of a source code line is one greater than the number of new-line characters read or introduced up to that point. Programmers could also assign line numbers to statements in older programming languages, such as Fortran, JOSS, and BASIC. In Fortran, not every statement needed a line number, and line numbers did not have to be in sequential order. The purpose of line numbers was for branching and for reference by formatting statements. Both JOSS and BASIC made line numbers a required element of syntax. The primary reason for this is that most operating systems at the time lacked interactive text editors; since the programmer's interface was usually limited to a line editor, line numbers provided a mechanism by which specific lines in the source code could be referenced for editing, and by which the programmer could insert a new line at a specific point. Line numbers also provided a convenient means of distinguishing between code to be entered into the program and direct mode commands to be executed immediately when entered by the user (which do not have line numbers). Largely due to the prevalence of interactive text editing in modern operating systems, line numbers are not a feature of most programming languages, even modern Fortran and Basic. In Fortran, as first specified in 1956, line numbers were used to define input/output patterns, to specify statements to be repeated, and for conditional branching. For example: DIMENSION ALPHA(25), RHO(25)

1. FORMAT(5F12.4)
2. READ 1, ALPHA, RHO, ARG SUM = 0.0 DO 3 I=1, 25 IF (ARG-ALPHA(I)) 4,3,3
3. SUM = SUM + ALPHA(I)
4. VALUE = 3.14159*RHO(I-1) PRINT 1, ARG, SUM, VALUE GO TO 2 Like assembler language before it, Fortran did not assume every line needed a label (line number, in this case).