3_2_10 Subroutines (procedures and functions)

You should be able to:

Understand the concept of subroutines.
Explain the advantages of using subroutines in programs.
Describe the use of parameters to pass data within programs.
Use subroutines that return values to the calling routine.
Know that subroutines may declare their own variables, called local variables, and that local variables usually:

•• only exist while the subroutine is executing

•• are only accessible within the subroutine.

Use local variables and explain why it is good practice to do so.

REVISE:

What is a subroutine?

Revisit 8_1_7 and 8_1_8.

Advantages of Subroutines

The key advantages of subroutines are:

It makes it easier to spot errors and fix them
It makes it easier to re-use code
The subroutine created can be used with other applications
It allows you to decompose the problem in a structured format
A large programming problem can be divided between programmers

Parameters

Parameter - The variable name for a value that is passed to a subroutine

Argument - The actual value that is passed to a subroutine

def add(a,b):

    c = a + b

    return (c)

print (add(5,3))

a and b are the parameters
5 and 3 are the arguments

Arguments are passed through the parameters to solve a problem. In this case, 5 and 3 are passed through the parameters and are added together.

Returning a Value (using functions)

We have returned a value in the example above. If I wanted to use that value then I could store it into a variable.

def add(a,b):

    c = a + b

    return (c)

c=(add(5,3))

print (c)

Local and Global Variables

When we look at scope of variables, there are two main types:

LOCAL - can only be viewed from within a sub-routine
GLOBAL - can be viewed by the entire application

The example function above contains a local variable called c. This variable can only be accessed from within the subroutine. If you deleted the line of code that reads c=(add(5,3)) then it would say that c doesn't exist.

PROGRAMMING CHALLENGE:

A menu of programs

Create a menu for all of the programs that you have developed so far. These could be:

Database created for 3_2_6
Password Storage program for 3_2_7
Password Encryption program for 3_2_8
Password Generator Machine for 3_2_9

The user should see a menu of the programs and be able to select which one they wish to run.

After running the program they should then return to the menu or quit.

TEST:

Download and print the test paper here: https://drive.google.com/open?id=0B5fLtQ0Xgr2Pd3JmZVJhd1JNaUU
Try the mock test yourself.
Use the 3.2.10 Walking Talking Mock below to guide you through answering the questions.

SOURCE RECOGNITION - PLEASE NOTE: The examination examples used in these walking talking mocks are samples from AQA from their non-confidential section of the public site. They also contain questions designed by TeachIT for AQA as part of the publicly available lesson materials.

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