Final answer:
The main difference between a function procedure and a sub procedure is that functions return a value and are used in expressions whereas subs do not return a value and are invoked to perform tasks without yielding a direct result.
Step-by-step explanation:
The main difference between coding a function procedure and coding a sub procedure is their ability to return a value. A function procedure is designed to perform tasks and return a value to the caller, which can then be used in expressions or assigned to a variable. In contrast, a sub procedure (short for "subroutine") is used to execute a sequence of statements but does not return a value directly.
Function procedures are ideal when you need to perform calculations or operations that yield a result necessary for other operations in your code. For instance, a function that calculates the sum of two numbers and returns the result you can use later. On the other hand, a sub procedure is better suited for tasks such as displaying a message to the user or resetting form fields, where a return value is not needed.
When you define a function, it must include a return type and typically contains a return statement. Functions are called as part of an expression, like so: let result = myFunction(arg1, arg2). For subs, however, you simply call them to perform the task with no need to handle any outcome or assign it to a variable: mySubProcedure(arg1, arg2).