Using Arrays

Referring to arrays

To refer to an entire array variable (for assignment, parameter, comparison, etc) just use the array variable name.

• Note: refer to the array variable, not the array type

To refer to an individual element in the array, you need to specify the array variable name and the index value for the element you want.

    PUT(coord1('b'));

    total := coord1('a') + coord1('b') + coord1('c');

    PUT(arr3(-2));

You need to be careful with the index value:

• using an index value outside the allowed range (defined in the array type declaration) causes a CONSTRAINT ERROR exception.
• eg PUT(coord1('z'));   *** WRONG ***

Remember, you refer to an element of the array variable, not of the array type.

An example program shows the use of an array to tally the number of times each lower-case letter appears in some text typed by the user.

You can find out some things about an array variable or array type by referring to the attributes of the array.

Operations on arrays

Assignment

You can assign one entire array variable to another of the same type

    coord1:= coord2;

Comparison

You can compare one array variable to another of the same type

• compares item by item

    if (coord1 /= coord2) then
        PUT("They are different");
    end if;

Arrays as Parameters

You can use an array variable as an actual parameter to a procedure or function.

The amount of flexibility you have in doing so depends on how the formal parameter was declared in the subprogram:

• if an unconstrained array type is used for the formal parameter, then any variable based on that type may be passed as an actual parameter.
• if a constrained array type is used for the formal parameter, then only variables of that type may be passed as an actual parameter

An example shows the benefit of using unconstrained array types for parameters.