Getting to know objects

The root term in OOP stems from objects, which are things. Essentially, the c1 and c2 variables in the PLC_PRG file are objects; they are different instances of the Calculator function block. In other words, the variables are compact copies of the function block. This is a very powerful concept because though the variables reference the same code in the function block, they can hold different data. To demonstrate this, match the following code snippet to your Calculator function block:

FUNCTION_BLOCK PUBLIC Calculator
VAR_INPUT
	input : INT;
END_VAR
VAR_OUTPUT
	output : INT;
END_VAR
VAR
END_VAR

In this demonstration, we have simple input and output variables. This code will require an input variable to be provided when the object variable is initialized. All the logic will do is assign the input to the output, as in the following snippet:

output := input;

To provide an argument to the function block, we have to use named parameters. As such, we are...