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 QuickSCREEN Details Example Contents Index |
| ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ |
| DIM Statement Details |
|
| Syntax |
| DIM [SHARED] variable[(subscripts)][AS type] |
| [,variable[(subscripts)][AS type]... |
| |
| Argument Description |
| SHARED The optional SHARED attribute allows all procedures |
| in a module to share arrays and simple variables. This |
| differs from the SHARED statement, which affects only |
| variables within a single SUB or FUNCTION. |
| |
| variable A BASIC variable name. |
| |
| subscripts The dimensions of the array. Multiple dimensions can be |
| declared. The subscript syntax is described below. |
| |
| AS type Declares variable to be an elementary or user-defined |
| type. The elementary types are INTEGER, LONG, SINGLE, |
| DOUBLE, and STRING (variable or fixed). |
| |
| |
| Subscripts in DIM statements have the following form: |
| |
| [lower TO] upper [,[lower TO] upper]... |
| |
| The TO keyword provides a way to indicate both the lower and the upper |
| bounds of an array's subscripts. The following statements are |
| equivalent (if there is no OPTION BASE statement): |
| |
| DIM A(8,3) |
| DIM A(0 TO 8, 0 TO 3) |
| DIM A(8,0 TO 3) |
| |
| With the TO keyword, you are no longer restricted to positive |
| subscripts. You can use TO to specify any range of subscripts |
| from -32,768 to 32,767: |
| |
| DIM A(-4 TO 10) |
| DIM B(-99 TO -5,-3 TO 0) |
| |
| If you use an array in your program without including the array in a |
| DIM statement, the maximum value of each subscript of the array is 10. |
| If you use a subscript that is greater than the specified maximum, an |
| error message appears that says "Subscript out of range." |
| |
| The DIM statement initializes all elements of numeric arrays to zero |
| and all the elements of string arrays to null strings. The fields of |
| record variables are initialized to zero, including fixed-string |
| fields. The maximum number of dimensions allowed in a DIM statement |
| is 60. |
| |
| If you try to dimension an array variable with a DIM statement |
| after you have referred to the array, an error message results that |
| reads "Array already dimensioned." It is good programming |
| practice to put the required DIM statements at the beginning |
| of a program, outside of any loops. |
| |
| Static and Dynamic Arrays |
| |
| How you declare an array also determines whether it is $STATIC |
| (allocated when the program is translated) or $DYNAMIC (allocated |
| when the program is run). |
| |
| ž An array declared first in a COMMON statement is $DYNAMIC. |
| ž Implicitly dimensioned arrays are $STATIC. |
| ž Arrays dimensioned with numeric constants or CONST statement |
| constants are $STATIC. |
| ž Arrays dimensioned with variables as subscripts are $DYNAMIC. |
| |
| The following list shows the different combinations and results: |
| |
| Statement Result |
| |
| DIM A(0 TO 9) The array A is allocated as a $STATIC array if |
| is $DYNAMIC not in effect. |
| |
| DIM A(MAXDIM) If MAXDIM is defined in a CONST statement A is a |
| $STATIC array. If MAXDIM is a variable, then the |
| array is a $DYNAMIC array and is only allocated |
| when the program reaches the DIM statement. |
| |
| Note: If the array size exceeds 64K, if the array is not dynamic, |
| and if the /AH option was not used, you may get an error message |
| that reads "Subscript out of range" or one that reads "Array |
| too big." Reduce the size of the array or make the array dynamic |
| and use the /AH command-line option. |
| |
| Type Declarations |
| |
| In addition to declaring the dimensions of an array, the DIM |
| statement may also be used to declare the type of a variable. For |
| example, the following statement declares the variable to be an |
| integer, even though there is no type declaration character or DEFINT |
| statement: |
| |
| DIM NumberOfBytes AS INTEGER |
| |
| The DIM statement provides a mechanism for declaring specific |
| variables to be records. In the following example, the variable |
| TopCard is declared as a record variable: |
| |
| TYPE Card |
| Suit AS STRING * 9 |
| Value AS INTEGER |
| END TYPE |
| |
| DIM TopCard AS Card |
| |
| You may also declare arrays of records: |
| |
| TYPE Card |
| Suit AS STRING * 9 |
| Value AS INTEGER |
| END TYPE |
| |
| DIM Deck(1 TO 52) AS Card |
| |
| Differences from BASICA |
| |
| BASICA executes a DIM statement when it encounters the statement in |
| the program. The array is only allocated when the statement is |
| executed, so all arrays in BASICA are dynamic. |
