Variables in BASIC are associated with either numeric or string values and, in the case of numeric variables, may be either simple variables or references to elements of one or two dimensional arrays; such references are called subscripted variables. Simple numeric variables shall be named by a letter followed by an optional digit. Subscripted numeric variables shall be named by a letter followed by one or two numeric expressions enclosed within pa- renthese s. 7.3 7.4 String variables shall be named by a dollar sign. letter followed by a Explicit declarations of variable types are not required; a dollar-sign serves to distinguish string from numeric variables, and the presence of scripted variable from a a subscript distinguisnes a simple one.
1. variable = numeric-variable / string-variable
2. numeric-variable = simple-numeric-variable / nume ric-array-elemen t
3. simple-numeric-variable = letter digit?
4. numeric-array-element = numeric-array-name subscript
5. numeric-array-name = letter
6. subscript = left-parenthesis numeric-expression (comma numeric-expression)? right-parenthesis
7. string-variable = letter dollar-sign X S$
A5 C$ V(3) W(X,X+Y/2)At any instant in the execution of a variable is associated with a single string-variable is associated with a The value associated with a variable program, a numeric- numeric value and a single string value, may be changed by the execution of statements in the program. The length of the character string associated with a string- variable can vary during the execution of a program from a length of zero characters (signifying the null or empty string) to 18 characters. Simple-numeric-variables and string-variables are declared implicitly through their appearance in a program. A subscripted variable refers to the element in the one or two dimensional array selected by the value(s) of the subscript(s). The value of each subscript is rounded to the nearest integer. Unless explicitly declared in a dimension statement, subscripted variables are implicitly declared by their first appearance in a program. In this case the range of each subscript is from zero to ten inclusive, unless the presence of an option-statement indicates that the range is from one to ten inclusive. Subscript expressions shall have values within the appropriate range (see 18). The same letter shall not be the name of both a simple variable and an array, nor the name of both a one-dimensional and a two- dimensional array. There is no relationship between a numeric-variable and a string- variable whose names agree except for the dollar-sign. At the initiation of execution the values associated with all variables shall be implementation-defined.
A subscript is not in the range of the explicit or implicit dimensioning bounds (fatal).
Since initialization of variables is not specified, and hence may vary from implementation to implementation, programs that are intended to be transportable should explicitly assign a value to each variable before any expression involving that variable is evaluated. There are many commonly us plementation-defined initi commended that all variabl sense that an exception wi the value of any variable assigned a value. ed alternatives for associating im- al values with variables; it is re- es are recognizably undefined in the 11 result from any attempt to access before that variable is explicitly