To specify the maximum values for array variable subscripts and allocate storage accordingly.
If an array variable name is used without a DIM statement, the maximum value of its subscript(s) is assumed to be 10. If a subscript greater than the maximum specified is used, a "Subscript out of range" error occurs.
The maximum number of dimensions for an array is 255.
The minimum value for a subscript is always 0, unless otherwise specified with the OPTION BASE statement.
An array, once dimensioned, cannot be re-dimensioned within the program without first executing a CLEAR or ERASE statement.
The DIM statement sets all the elements of the specified arrays to an initial value of zero.
10 DIM A(20) 20 FOR I=0 TO 20 30 READ A(I) 40 NEXT I
This example reads 21 DATA statements elsewhere in the program and assigns their values to A(0) through A(20), sequentially and inclusively. If the A array is single precision (default accuracy) then line 10 will allocate 84 bytes of memory to this array (4 bytes times 21 elements).