| .CONST Statement Details. |
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| CONST Statement Details |
|
| Syntax |
| CONST constantname = expression [,constantname = expression]... |
| |
| Argument Description |
| constantname A name following the same rules as a BASIC variable |
| name. You may add to the name a type-declaration |
| character (%, &, !, #, or $) to indicate its type, |
| but this character is not part of the name. |
| |
| expression An expression consisting of literals (such as 1.0), |
| other constants, or any of the arithmetic and |
| logical operators except exponentiation (^). You may |
| also use a single literal string such as "Error on |
| input". You cannot use string concatenation, |
| variables, user-defined functions, or intrinsic |
| functions like SIN or CHR$ in expressions assigned |
| to constants. |
| |
| If you use a type-declaration character in the name, you may omit the |
| character when the name is used, as shown in the following example: |
| |
| CONST MAXDIM% = 250 |
| . |
| . |
| . |
| DIM AccountNames$(MAXDIM) |
| |
| If you omit the type-declaration character, the constant is given a |
| type based on the expression in the CONST statement. Strings always |
| yield a string constant. With numeric expressions, the expression is |
| evaluated and the constant is given the simplest type that can |
| represent the constant. For example, if the expression gives a result |
| that can be represented as an integer, the constant is given an |
| integer type. |
| |
| Note: Names of constants are not affected by DEFtype statements |
| such as DEFINT. A constant's type is determined either by an |
| explicit type-declaration character or by the type of the |
| expression. |
| |
| Constants must be defined before they are referenced. The following |
| example produces an error because the constant ONE is not defined |
| before it is used to define TWO (constants are defined from |
| left to right): |
| |
| CONST TWO = ONE + ONE, ONE = 1 |
| |
| Constants declared in a SUB or FUNCTION are local to the |
| SUB or FUNCTION. A constant declared outside a procedure |
| is defined throughout the module. You can use constants anywhere that |
| you would use an expression. |
| |
| A common programming practice is to use a statement like the following |
| (recall that any nonzero value represents "true"): |
| |
| TRUE=-1 |
| |
| Constants offer several advantages over using variables for constant |
| values: |
| |
| ž Constants need to be defined only once for an entire module. |
| ž Constants cannot be inadvertently changed. |
| ž In stand-alone programs, using constants produces more efficient |
| code than using variables. |
| ž Constants make programs easier to modify. |
| |
