Editing BASIC-PLUS (section)

===Variables, expressions and matrixes===
Variable names in the early versions of BASIC-PLUS could be a single letter or a single letter followed by a single digit.{{sfn|PLUS|1972|p=2-6}} With the inclusion of "Extend mode" in later versions, variable names could be up to 29 characters long, and dot (.) was added as a permitted character. Every variable name still had to begin with a letter.{{efn|Before the introduction of Extend mode, white space was not required between variables and other language elements: {{code|1=FOR I=STOP}} would be interpreted as {{code|1=FOR I = S TO P|2=basic}}.}} As in most versions of BASIC, the {{code|LET}} keyword, for variable assignment, was optional. It could set multiple variables to a single value, like {{code|1 = LET A,B,C=10|2=basic}}.{{sfn|PLUS|1972|p=3-3}}

The language supported three data types; floating-point numbers, integers, and strings. Variables with no suffix were floating point (8 bytes, range 0.29{{x10^|-38}} to 1.7{{x10^|38}}, up to 16 digits of precision). Integer variables (16-bit, range &minus;32768 to +32767) were indicated with a {{code|%}} suffix,{{sfn|PLUS|1972|p=6-1, 6-2}} string variables (variable length) were indicated with a {{code|$}} suffix.{{sfn|PLUS|1972|p=5-2}}

The list of mathematical and logical operators was typical of most BASICs, with some extensions. For math, {{code|+}}, {{code|-}}, {{code|*}}, {{code|/}} and {{code|^}} were supported, along with {{code|**}} as an alternate form of {{code|^}} for [[computer terminal]]s that might not have that character. Standard logical comparisons were {{code|{{=}}}}, {{code|<}}, {{code|>}}, {{code|<{{=}}}}, {{code|>{{=}}}}, and {{code|<>}}. One interesting addition was the {{code|{{=}}{{=}}}} operator, for "approximately equal". This would return true if the two numbers would be printed the same, that is, their six most significant digits were the same.{{sfn|PLUS|1972|p=2-9}} Logical operators included the typical {{code|NOT A}}, {{code|A AND B}} and {{code|A OR B}}, along with {{code|A XOR B}}, {{code|A EQV B}} which return true if both A and B are true or both are false, and {{code|A IMP B}} which is false if A is true and B is false and otherwise always true.{{sfn|PLUS|1972|p=2-10}}

The {{code|DIM}} statement could allocate one-dimensional and two-dimensional arrays of any of the three data types. The range of subscripts always began with 0 (but {{code|MAT}} statements did not set elements in row 0 or column 0).{{sfn|PLUS|1972|p=3-21}}{{sfn|PLUS|1972|p=5-3}}

The language also included a number of {{code|MAT}} commands to work with the entire array (or MATrix). The {{code|MAT READ}} command would fill the matrix with values in a {{code|DATA}} statement,{{sfn|PLUS|1972|p=7-2}} {{code|MAT INPUT}} would fill the array with user-typed values, and {{code|MAT PRINT}} would print out the elements in a 1D or 2D format.{{sfn|PLUS|1972|p=7-3}} {{code|MAT}} could also be used to set default values in a matrix using associated keywords, for instance, {{code|1 = MAT A=ZER}} would fill the A array with zeros.{{sfn|PLUS|1972|p=7-5}} {{code|TRN}} would transpose an entire matrix, and {{code|INV}} would invert it.{{sfn|PLUS|1972|p=7-7}} Additionally, {{code|+}}, {{code|-}}, and {{code|*}} could be used on matrixes, performing the associated matrix operation.{{sfn|PLUS|1972|p=A-1}}