Editing Dartmouth BASIC (section)

==Examples==
Early versions of BASIC did not have the ability to read and write external files. To represent lists of data that would normally be read from a file, BASIC included the <code>DATA</code> keyword, which could be followed by an arbitrarily long list of elements, ending only at the limit of the line length. The <code>DATA</code> was non-executable and was skipped if encountered. <code>READ</code> commands would consume the data one by one, keeping track of its location within the complete collection of <code>DATA</code> elements in an internal pointer. In version 3, a <code>RESTORE</code> command was added to reset the pointer to the first <code>DATA</code> command in a program.

In this example, "the first three data values are read into X, Y, and Z respectively. The value -1 is read into N. The next 11 values, .1 through .3, are read into the 11 elements of array B."<ref>{{cite book|title=BASIC Language Reference Mandual|date=January 1975|publisher=Interdata|pages=3–24}}</ref>

<syntaxhighlight lang="basic">
15 READ X, Y, Z
20 READ N
24 FOR I=0 TO 10
25 READ B(I)
26 NEXT I
40 DATA 4.2, 7.5, 25.1, -1, .1, .01, .001, .0001
45 DATA .2, .02, .002, .0002, .015, .025, .3, .03, .003
</syntaxhighlight>

Unlike most subsequent BASICs, Dartmouth BASIC, from the Third Edition onwards, had a matrix keyword, <code>MAT</code>, which could prefix a number of other commands to operate on entire arrays of data with a single command. In this example, from the 1968 manual,<ref>[http://www.bitsavers.org/pdf/dartmouth/BASIC_4th_Edition_Jan68.pdf BASIC, 4th Edition, 1968], page 53</ref> <code>MAT INPUT V</code> is used to input a series of variables. When the user enters nothing on a line, this process ends and the total number of elements is accessed in the <code>NUM</code> pseudovariable.{{efn|Why <code>NUM</code> was not implemented as a function, like <code>LEN()</code>, is a mystery.}} The code then adds up all of the individual elements in the matrix and calculates the average. The Third Edition also added indentation, which is used here to clarify the loop structure.

<syntaxhighlight lang="basic">
5 LET S = 0 
10 MAT INPUT V 
20 LET N = NUM 
30 IF N = 0 THEN 99 
40 FOR I = 1 TO N 
45   LET S = S + V(I) 
50 NEXT I 
60 PRINT S/N 
70 GO TO 5 
99 END
</syntaxhighlight>