Declaring Variables and Parameters in User Functions

Variables in user functions are used to assist in calculations, and/or serve as the function parameters.

Variables as Parameters

Variables in a user function that are declared with the VAR_INPUT, VAR_OUTPUT, and VAR_IN_OUT keywords make up the function's parameters. The order in which the parameters are declared in the user function is the order in which the parameters must be entered when calling that user function.

Input Parameters (VAR_INPUT)

Input parameters can only be read from. Values cannot be assigned to input parameters.

Output Parameters (VAR_OUTPUT)

Output parameters can only be assigned to. That is, output parameters can only be used on the left-hand side of assignment expressions.

Input/Output Parameters (VAR_IN_OUT)

Input/output parameters can be read and written.

Variables as Local Variables

Variables declared with the VAR keyword are variables that can be used locally in the user function to assist in calculations.

Declaring Variables and Parameters

Use the format in the example below to declare variables in user functions. Keep in mind that the order in which the parameters (VAR_INPUT, VAR_OUTPUT, and VAR_IN_OUT) are declared in the user function is the order in which the parameters must be entered when calling that user function.

Variables can be of any data type, and can be fixed-length arrays.

Local variables (VAR), output parameters (VAR_OUTPUT), and input/output parameters (VAR_IN_OUT) can optionally be initialized upon declaration.

Examples

VAR_INPUT

MyInputVar : REAL;

MyOtherInputVar : DINT;

YourVar : Array [0..4] OF REAL;

END_VAR

VAR_IN_OUT

MyInOutVar : REAL;

END_VAR

VAR_OUTPUT

MyOutputVar : REAL :=4;

MyArray : Array [0..3] OF REAL := [10, 10, 0];

END_VAR

VAR

MyVar : REAL := 100;

YourVar : Array [0..9] OF DINT;

END_VAR

Declaring Arrays

Array bounds are specified in brackets [], with two intermediate periods (..). The array bounds can be any integer value, including negative values. For most applications, the lower bound is zero. The maximum length of an array in a user function is 32 elements.

Parentheses can be used a repetition factor when assigning an initial value. The value preceding the parentheses specifies the number of repetitions. For example, [4(0)] is equivalent to [0,0,0,0], and [1,3(99),1] is equivalent to [1,99,99,99,1].

Example

This declaration creates an output array of length 5, with initial values of [-1,1,0,0,0].

VAR_OUTPUT

MyArray : Array [0..4] OF REAL := [-1,1, 3(0)];

END_VAR