42. OCR A Level (H046-H446) SLR8 - 1.2 Introduction to programming part 3 procedures & functions

Summary

In this segment of a programming video series, the focus is on subroutines, procedures, and functions. Subroutines are blocks of code with unique names that simplify complex problems into manageable parts, aiding in code writing, debugging, and reuse. Procedures are subroutines that perform tasks without returning values, while functions perform tasks and return values. In object-oriented programming, these are known as methods. The video uses a Python program to illustrate how subroutines are called and executed, highlighting their role in making code modular, reusable, and easier to test. It also touches on pseudocode formatting for exams and the benefits of using subroutines.

Takeaways

• 💡 A subroutine is a block of code with a unique name that simplifies programming by breaking down complex problems into smaller, manageable tasks.
• 🔍 The term 'subroutine' encompasses two concepts: 'procedures', which are blocks of code that perform a task, and 'functions', which perform a task and return a value.
• 📚 In object-oriented programming, subroutines are referred to as 'methods', which can either return a value or not, similar to functions and procedures.
• 👀 Subroutines in a program are typically defined at the top, with the main program starting at the bottom, making the structure clear and organized.
• 🔑 The main program calls subroutines, which are executed in sequence until completion, after which control returns to the main program.
• 🎯 Procedures and functions are fundamental to programming, with functions being a type of subroutine that returns a value, useful for calculations and data manipulation.
• 🧩 Subroutines promote code reusability, making it easier to maintain and test programs, as they can be grouped into libraries for use across different programs.
• 📝 The script introduces a Python program example to illustrate how subroutines are defined and called within a program, emphasizing practical application.
• 🔄 Flowcharts use specific symbols to represent the calling of subroutines, showing the flow of control between different parts of a program.
• 📖 For exams, students are not expected to memorize pseudocode syntax but should be familiar with it, as exam questions might use unfamiliar syntax.

Q & A

What is a subroutine?

A subroutine is a block of code given a unique, identifiable name within a program. It is used to break down a larger problem into smaller, more manageable problems, making the code easier to write, debug, and reuse.

What is the difference between a procedure and a function?

Procedures are blocks of code that carry out a set task, while functions are blocks of code that carry out a set task and also return a value.

In the context of object-oriented programming, what are procedures and functions called?

In object-oriented programming, procedures and functions are referred to as methods. Methods can either return a value or not.

How are subroutines identified in a program?

Subroutines can be identified as they start with either the word 'procedure' or 'function' and end with 'end procedure' or 'end function'.

What is a procedure call?

A procedure call is when a program jumps to a subroutine with the same name and starts executing the code inside it until it reaches the end, at which point it returns to the place where it left off originally.

Why are subroutines useful in programming?

Subroutines are useful because they make programs easier to write and debug, create reusable components, can be grouped in libraries for easy reuse across different programs, and make programs easier to test.

How does a function differ from a procedure in terms of its execution?

A function differs from a procedure in that it returns a value, which is typically the contents of a variable at the point of return, whereas a procedure does not return a value.

What is the purpose of the 'import random' line in the provided Python program?

The 'import random' line imports the random library of functions into the program, allowing the use of its functionalities within the program.

What is pseudocode and why is it used in exams?

Pseudocode is a high-level description of the operating logic of a program or other algorithm. It is used in exams to provide a familiar format for learners, regardless of the programming language they have been learning, to demonstrate their understanding of programming concepts.

Why is it important for students to be familiar with the language guide used in external assessments?

It is important for students to be familiar with the language guide used in external assessments to understand the format and syntax that procedures and functions will be displayed in during the exams, even if they are not expected to memorize or replicate the exact syntax.

How does the use of subroutines affect the main program's code?

The use of subroutines typically results in the main program having very little code, with most of the functionality contained in separate blocks or subroutines, which are called from within the main program.

Outlines

00:00

💻 Understanding Subroutines in Programming

This paragraph introduces the concept of subroutines in programming, explaining that they are blocks of code with unique names used to simplify complex problems into smaller, more manageable tasks. It differentiates between procedures, which are subroutines that perform tasks, and functions, which are subroutines that also return a value. The paragraph further clarifies that in object-oriented programming, these are known as methods. It also discusses the typical structure of a program where subroutines are defined at the top and the main program at the bottom, illustrating how a program executes by calling these subroutines. The paragraph concludes with an example of a program with four procedures and explains how the main program interacts with these subroutines through procedure calls.

05:00

🎲 Exploring Procedures and Functions in Python

The second paragraph delves into a Python program to demonstrate the practical application of procedures and functions. It explains how a function differs from a procedure by returning a value. The paragraph walks through the program's execution, highlighting how the program jumps to different subroutines upon function calls and returns to the main program after completing the subroutine's execution. It also touches on the benefits of using subroutines, such as ease of writing and debugging, reusability, and the ability to group them into libraries. The paragraph emphasizes the importance of understanding the flow of control in programs, including the use of flowcharts to visualize the calling of subroutines. It concludes with a note on the language guide used in external assessments, advising students to familiarize themselves with the syntax of procedures and functions as they may appear in exams, even if they are not required to memorize or replicate the exact syntax.

10:00

📚 Additional Resources for Programming Education

The final paragraph offers guidance on additional resources for learning programming, suggesting that students download a copy of the specification and print out the appendix for reference. It mentions that schools with a specific subscription can provide students with a student learning and exam support guide, which contains valuable reference materials. The paragraph concludes with a musical note, indicating the end of the video script.

Keywords

💡Subroutine

A subroutine is a segment of code that can be reused throughout a program. It is defined by a unique name and can be called from different parts of the program to perform a specific task. In the context of the video, subroutines are used to break down complex problems into smaller, more manageable ones, thereby simplifying the coding process. The script mentions that subroutines are written at the top of the program and are called from the main program, which is typical programming practice.

💡Procedure

A procedure is a type of subroutine that performs a specific task but does not return a value. It is a block of code that is executed when called. In the video script, procedures are described as a broad concept that includes methods in object-oriented programming. The script provides examples of procedures named 'initialize', 'output 1', 'output 2', and 'adjust', which are called from the main program.

💡Function

A function is a type of subroutine that not only performs a task but also returns a value. This is a crucial aspect that differentiates functions from procedures. In the video, functions are shown to be called within the main program and other subroutines, with examples like 'output throw' and 'order dice', which return values and thus influence the flow of the program.

💡Object-Oriented Programming (OOP)

Object-oriented programming is a programming paradigm that uses objects and classes. In OOP, procedures and functions are often referred to as methods. Methods are associated with objects and can manipulate the object's data. The video script mentions that in OOP, whether a method returns a value or not is a key consideration, similar to the distinction between procedures and functions.

💡Method

In the context of object-oriented programming, a method is a function or procedure that is associated with an object. Methods can modify the state of an object or return information about an object. The video script explains that methods can be thought of in similar terms to procedures and functions, but they are used within the context of classes and objects.

💡Main Program

The main program is the primary section of code that runs when a program is executed. It often contains the entry point of the program and coordinates the execution of various subroutines. In the video, the main program is depicted as starting at the bottom of the code and calling various subroutines, such as 'initialize' and 'output 1', to perform tasks.

💡Procedure Call

A procedure call is the act of invoking a procedure from within a program. This causes the program to pause its current execution, jump to the procedure's code, and execute it. The video script illustrates this with the 'initialize' procedure call, which is the first line of executable code in the program, highlighting how the program execution jumps to the subroutine and then returns.

💡Return Statement

A return statement is used in functions to send back a value to the caller. It is a key feature of functions that differentiates them from procedures. In the video script, the 'output throw' function is shown to use a return statement to pass the value of a variable back to the main program, demonstrating how functions can influence the program's logic through returned values.

💡Code Reusability

Code reusability refers to the ability to use the same code in different parts of a program or in different programs. Subroutines, procedures, and functions enhance reusability by encapsulating functionality, which can then be called multiple times without rewriting the code. The video emphasizes the benefits of subroutines in creating reusable components that can be grouped into libraries for easy reuse.

💡Flowchart

A flowchart is a diagrammatic representation of the flow of a program, showing the steps and decisions in a visual format. In the video, flowcharts are mentioned as a way to represent the calling of subroutines, with a specific symbol indicating where the program should jump to execute another flowchart and then return to the calling flowchart.

💡Pseudocode

Pseudocode is an informal high-level description of the operating principle of a computer program or other algorithm. It is used to outline the structure of a program without getting into the details of the actual coding syntax. The video script notes that learners are not expected to memorize the syntax of pseudocode but should be familiar with it to understand exam questions, which may use unfamiliar syntax.

Highlights

Subroutines are blocks of code with a unique name used to break down larger problems into smaller ones.

Subroutines make code easier to write, debug, and reuse.

The term 'subroutine' covers procedures and functions.

Procedures are blocks of code that carry out a task.

Functions are blocks of code that carry out a task and return a value.

In object-oriented programming, procedures and functions are referred to as methods.

Methods can return a value or not, similar to functions and procedures.

Subroutines are identified by starting with 'procedure' or 'function' and ending with 'end procedure' or 'end function'.

The main program typically starts at the bottom of the code, after the subroutines.

A procedure call is used to execute code within a subroutine.

When a subroutine is called, the program jumps to it, executes its code, and then returns to the main program.

The main program contains logic and calls to various subroutines.

Subroutines help to minimize the amount of code in the main program.

Procedures and functions are demonstrated in a worked example using Python.

OutputThrow is a function that returns a value and includes calls to other subroutines.

RollADice and OrderDice are functions that return values based on dice outcomes.

Subroutines allow for code reusability and can be grouped into libraries.

The 'random' library is imported to provide additional functions for the program.

Subprograms are called from within flowcharts using a specific symbol indicating a jump to another chart.

Exam questions may use unfamiliar syntax, but understanding the concept is key.

Appendix 5d of the specification provides a guide to the format of pseudocode used in exams.

Learners are not expected to memorize pseudocode syntax but should understand its meaning.

A student learning and exam support guide is available for additional reference.

Transcripts

this is part 3 of 6 of our video series

on the introduction to programming

in this video we look at subroutines

procedures and functions

so what actually is a subroutine well

it's nothing more

than a block of code given a unique

identifiable name within a program we

use subroutines to help us break down a

larger problem

into a series of smaller more manageable

problems

thus making the code easier to write

debug and reuse

the word subroutine is a generic term

and in a broad sense it covers two

concepts you need to know about

procedures those are blocks of code that

carry out a set task

and functions blocks of code that carry

out a set task

and in addition return a value

if you're thinking about

object-orientated programming we still

have procedures and functions

but in that context they're referred to

as methods

methods can either return a value or not

return a value

and so you can think of them in very

similar terms

but let's just have a brief look at a

program here

the first thing you will notice is there

are multiple

blocks of code or subroutines in fact we

have

four in the exam

you'll be able to spot subroutines as

they will start with either the word

procedure

or function and end with either

end procedure or end function

after the initial word you can then see

a name is given to that procedural

function

which uniquely identifies it in the

program

so this program has four procedures

called initialize

output 1 output 2 and adjust

you'll notice the actual main program

starts down the bottom

and this is quite typical that the

blocks of code the subroutines are

written at the top of the program

and your main program starts towards the

end so when we actually run this program

it starts at this line or strictly

speaking this is a comment so

it will start at the next line

the very first line of code in this

program therefore

is initialize open brackets close

brackets

this is what we call a procedure call

a call to another procedure

as soon as the program hits this line of

code it

searches for a subroutine with the same

name and then it

jumps to the code inside that subroutine

the program carries on executing the

code in that subroutine

until it reaches the end at which point

it returns to the place where it left

off originally

so in this case we go back to the main

part of the program at the bottom there

and we continue with the next line which

is the while line

in a similar fashion you can see the

main program

contains three other calls to procedures

and again each time we hit one of those

we would jump off to the appropriate

subroutine execute the code inside it

and then return in this way you'll

notice the actual main program itself

now has very little code it has some

logic in the form of a while loop

but most of the code is actually

contained elsewhere

in blocks of code this is a typical way

of programming

okay so now we've gone over the basics

let's actually look at a worked example

of procedures and functions

in the following python program so a

quick recap then we have two main types

of subroutines

there's procedures that carry out a task

and functions that carry out a task and

return a value

so the first thing to notice here with

this program is it actually

starts towards the very bottom of the

code listing

under the comments where it says main

program

the rest of the program is constructed

blocks

or subroutines

now you'll notice one of the very first

lines of code that's run

is print output throw

output throw is a call

to a subroutine

so what happens is when we reach output

throw

we search the rest of the code for a

subroutine with a matching name

we find one and so the code jumps

to that section of the program and

starts executing in sequence from that

point on

when the program reaches the end we can

see

it says return a value return the

contents of the variable

role at this point the program jumps

back

to where it left off before it entered

this subroutine because we're returning

a value

we know that this subroutine is actually

a function

you'll notice that as part of executing

the function

output throw we also have a call

to another sub program roll a dice

so again we would jump off at that point

to the subroutine roll a dice and we can

see again here

that roller dice returns a value

thus again making this a function

again a little bit further in the output

throw function

we see another call to a subroutine

this one called order dice so as soon as

we hit that line of code

the program jumps off to the order die

subroutine

and starts executing the code in there

again depending on the result of the if

statement if d1 is greater than equal d2

we hit one of two return statements

one of the other is going to get

executed and when we do that

we'll jump back into the output throw

function

and of course once again because order

dice returns a value

this is a function and not a procedure

so what are the advantages then of using

subroutines such as those shown

well programs are easy to write and

they're easy to debug

it creates reusable components

these functions can also be grouped in a

library

for easy reuse across many different

programs

indeed you do that in this program here

and you may have done something similar

in your own programs

the first line of code says import

random

and this imports the random library of

functions

into our program so we can then make use

of them

finally programs are simply easier to

test

if they're written in modules and blocks

of code

here we can see how subprograms are

called from inside flowcharts

there's a specific symbol used in

flowcharts

which tells you that you need to jump

off and start

executing another flowchart and when you

reach the

end of that flowchart you'd return from

the one that called it

and carried on so this is the flow chart

for the previous program we showed you

in python

pause the video for a second and just

work through it slowly

so you can see how you jump back and

forwards between the different flow

charts

as they're being called

now the example we work through here is

in python and you may all be using a

different language at a level such as c

sharp or java

but it's worth pointing out the format

that procedures and functions

will be displayed in in the ocr exams

so here you can see the syntax that they

will use for a procedure

and indeed for a function

so having watched this video you should

be able to answer the following key

question

what is the difference between a

procedure and a function

we're just going to go over a quick note

now about the language guide that's

used in your external assessments

so remember the example don't know what

language you've been learning to program

so exam questions might use an

unfamiliar syntax

towards the back of the specification

for both a s and a level you'll find

appendix 5d where the exampled state

the following guide shows the format

pseudo code will appear

in the examined components is provided

to allow

you to give learners familiarity before

the exam

learners are not expected to memorize

the syntax of the pseudocode

and when asked may provide answers in

any style of pseudo code they choose

providing its meaning could be

reasonably inferred

by a competent programmer

so although you don't have to answer in

the specific syntax shown in the exam

papers so you are familiar not thrown in

the exam

it's worth downloading a copy of the

specification and printing out the

appendix

if your school is a craving day

subscriber then ask your teacher for a

copy of our student learning

and exam support guide this provides all

the information you need

in a set of handy reference sheets

[Music]

you