Subroutines and structured programming

Overview

Procedures and functions, parameters and return values, local variables, clear interfaces, and why subroutines and the structured approach make programs easier to write, share and debug.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a subroutine?

   Model answer

   A subroutine is a named block of code that carries out a specific task. The subroutine sits outside the main program and runs only when it is called.

2. 2

   How is a subroutine called?

   Model answer

   A subroutine is called by writing its name in a program statement, with any parameters in brackets. Control passes to the subroutine, then returns to the next statement once it finishes.

3. 3

   What is the difference between a procedure and a function?

   Model answer

   A function returns a value to the code that called it. A procedure carries out a task but does not return a value.

4. 4

   What is a parameter?

   Model answer

   A parameter is a value passed into a subroutine when it is called. The subroutine uses the parameter as data to work on.

5. 5

   If SUBROUTINE area(w, h) holds RETURN w * h, what does area(4, 3) return?

   Model answer

   The call area(4, 3) returns 12. The parameter w takes the value 4 and h takes the value 3.

6. 6

   What is a return value?

   Model answer

   A return value is data passed back from a subroutine to the code that called it. The RETURN statement sends the value back.

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