This is my lecture slides on Introduction to Programming. I have used several sources for the slides, including "Java How to Program" by Deitel

1. Nadim Ahmed
Introduction to
Programming
01 – Programming and Algorithms
Nadim Ahmed

2. Nadim Ahmed
Introduction
• You must bring a pen and some paper
with you to write notes from the board.
• This is a challenging subject, so do come
to all lectures and labs, and make plenty
of notes.
• If you have any questions, then please
ask.

3. Nadim Ahmed
How to Learn
• I will give you exercises to do, so please
do them.
• You will NEVERNEVERNEVERNEVER learn programming by
memorising!
• Make sure you understandunderstandunderstandunderstand what is
happening.
• You must attempt the exercises by
yourself.

4. Nadim Ahmed
What is a Computer?
“They don’t get angry, they don’t get
happy, they don’t get sad, they don’t
laugh at your jokes. They just run
programs.”
Paraphrased from “Short Circuit”

5. Nadim Ahmed
What is a Computer?
• Let us start at the beginning and see
what is a computer.
• A computer is a machine that can
calculate and use logic to carry out
tasks.

6. Nadim Ahmed
What is a Computer
• Computers take in inputinputinputinput.
– This is data that is given to the computer.
• They processprocessprocessprocess the input.
– This is when they manipulate/use the data.
• They produce an outputoutputoutputoutput.
– This is the result of manipulating the input.

7. Nadim Ahmed
What is Programming?
• To get a computer to carry out different
tasks, we have to be able to give it
specific instructions.
• This is programming.
• Before we start programming, we have
to look at something else.

8. Nadim Ahmed
Algorithms
• Before writing a program, the
programmer must understand what the
result should be and how the program
will produce it.
• It is important to know that a computer
program describes a computational
procedure called an algorithm.

9. Nadim Ahmed
Algorithms
• An algorithm is a step by step sequence
of instructions that describes how to
perform a computation.
• An algorithm answers the question
– “What method will you use to solve this
computational problem?”

10. Nadim Ahmed
Algorithms
• Only after
– we clearly understand the desired result,
– we clearly understand the algorithm and
– know the specific steps required to produce
the desired result
• we can write the program.

11. Nadim Ahmed
Programming
Programming is the translation of
the selected algorithm into a
language that the computer can
use.

12. Nadim Ahmed
Programming
Let’s see a real life example of what is
programming.

13. Nadim Ahmed
Programming a Sponge Cake
• Switch oven on at 180°C
• Cream together 225g softened butter
and 225g of sugar
• Whisk 4 eggs and add to mixture slowly
• Add 225g of sifted self raising flour and
fold.
• Grease two cake tins and add mixture.
• Bake for 20 – 30 minutes until golden
brown.

14. Nadim Ahmed
Programmable Computer
• Can provide a computer a sequence of
instructions describing the process I
want it to execute.
• Have a fixed set of primitives, can
program almost anything.
– In our sponge cake, the primitives are
commands like
•Cream, whisk, fold, grease.

15. Nadim Ahmed
Programming and Algorithms
• To illustrate an algorithm, we will
consider a simple requirement.
• Assume that a program must calculate
the average of three numbers.
• Most people do not think
algorithmically;
– They tend to think intuitively.

16. Nadim Ahmed
Programming and Algorithms
• If your car tyre needs changing,
– you will not think of all the steps required,
– you will either simply change the tyre or
– call someone else to do the job.
• This is an example of intuitive thinking.

17. Nadim Ahmed
Programming and Algorithms
• Unfortunately, computers do not
respond to intuitive commands.
• A general statement such as “find
average of three numbers” means
nothing to a computer.
– This is because computers can only respond
to algorithmic commands written in an
acceptable language such as C.

18. Nadim Ahmed
Programming and Algorithms
• To program a computer successfully, you
must clearly understand the difference
between algorithmic and intuitive
commands.
• You must give the computer a detailed,
step-by-step set of instructions that
forms an algorithm.

19. Nadim Ahmed
Average of Three Numbers
• We have to understand what the
requirements are, and what the result
will be.
• To make it easier, let us identify the
three numbers to use as an example.

20. Nadim Ahmed
Average of Three Numbers
• We have chosen the numbers
• 2, 3 and 10
Class Discussion:Class Discussion:Class Discussion:Class Discussion:
What do we mean by “find the average of
2, 3 and 10”?

21. Nadim Ahmed
Average of Three Numbers
• To find the average, we add up 2, 3 and
10.
• Then we divide that by three.
• 2 + 3 + 10 = 15
• 15 ÷ 3 = 5
• Therefore the average is 5.

22. Nadim Ahmed
Average of Three Numbers
• We now know how to find the average of
three specific numbers.
• How are we going to make it a bit more
general?
• Think of what steps you will take to get
the average of three numbers.

23. Nadim Ahmed
Average of Three Numbers
Class Discussion:Class Discussion:Class Discussion:Class Discussion:
What do we need to make a generic
program to find the average of three
numbers?

24. Nadim Ahmed
Average of Three Numbers
• We need to get our three numbers.
• We need to add the three numbers
• We need to divide the total by 3.

25. Nadim Ahmed
Code Modularity
• When programming, we break our large
problem into modules
– where each module can be thought of as a
single task.
• These modules make it easier to break
down programming problems.

26. Nadim Ahmed
Making Pizza
When making pizza, we have four basic tasks.
• Make pizza base.
• Make pizza topping.
• Assemble topping on the base.
• Bake pizza in oven.
Each of these tasks can be thought of as a
modulemodulemodulemodule, as they perform one task each.

27. Nadim Ahmed
Why Modules?
• Programs that use modules are known as
modular programsmodular programsmodular programsmodular programs.
• Modular programs are easier to develop,
correct and modify.
– Since they split the tasks into separate
modules, you can deal with each module
individually.
– If you have a mistake in one module, you
don’t worry about it affecting other modules.

28. Nadim Ahmed
Modules
• Each module is actually a small
subprogram.
• We break our module into smaller tasks.
• Each module
– InputInputInputInputs some data.
– ProcessProcessProcessProcesses the data.
– OutputOutputOutputOutputs the processed data.

29. Nadim Ahmed
A Pizza Module
• For our pizza making program, let’s see
our module “Make pizza topping”.
• Let’s say the topping will be a “cheese
and tomato” topping.
• What will the input, process and output
of the module be?

30. Nadim Ahmed
Make Pizza Topping
• Input
– Cheese
– Tomato
– Garlic
– Green Peppers
– Basil
– Onion

31. Nadim Ahmed
Make Pizza Topping
• Process
– Gently heat up tomato, garlic, green
peppers, basil and onion.
– Blend the mixture
– Grate the cheese and keep aside.
• Output
– Tomato sauce
– Grated cheese

32. Nadim Ahmed
Add Module
Class DiscussionClass DiscussionClass DiscussionClass Discussion
• If we have a module that adds two
numbers.
• What are the
– Inputs?
– Processes?
– Outputs?

33. Nadim Ahmed
Add Module
• Inputs
– Our two numbers that we want to add.
– Let’s call them a and b
• Process
– Add the two numbers and keep the result
safe.
c = a + b
• Output
– The result which is stored in c

34. Nadim Ahmed
Modules
Class DiscussionClass DiscussionClass DiscussionClass Discussion
• We have a program that can convert between
different types of distances.
• These can be
– kilometres to miles,
– miles to kilometres,
– inches to centimetres,
– centimetres to inches.
• If we have a program that converts different
types of distances then we should break it
down into modules.
– What modules do we use?

35. Nadim Ahmed
Programming and Modules
• We can have one module that converts
from kilometres to miles, and another
one to convert from miles to kilometres.
• Also, we can have one module that
converts from centimetres to inches and
vice versa.
• In other words, one module for each
task.

36. Nadim Ahmed
How Will We Program the
Computer?
• We will now look at how we will
program the computer.
• We need to communicate with the
computer so then we are understood by
the computer.
• I am speaking to you in English, which
some of you understand.
• We will now explore languages that
humans can use with computers.

37. Nadim Ahmed
Levels of Languages
• Computers work in binary
– 0, 1
– Not very human readable.
• To make things easier, we have various
levels of languages.
• These levels range from
– HighHighHighHigh to
– LowLowLowLow

38. Nadim Ahmed
Levels of Languages
• Machine code is the lowest level of
programming language.
– This is the language that the CPU uses.
– Tailored for each individual CPU.
– If you write something for an ARM
processor, it will not work on an Intel
processor.

39. Nadim Ahmed
Multiplying in Low Level
• This is an example of multiplying two
numbers in a low level language.
• It has been written for the Zilog Z80
microprocessor, which was very popular
in the late 1970s until late 1980s.
• There was no multiply command, so we
had to add numbers several times.

40. Nadim Ahmed
Multiplying Two Numbers
org &4000 ; store in memory location 4000
ld b,3 ; load register b with 3
ld a,0 ; load register a with 0
; The following line is in memory location 4004
add a,2 ; add 2 to register a
dec b ; decrement register b by 1.
jp nz,&4004 ; jump if not zero to memory location 4004
ld (&400f),a ; Copy content of register a to location 400f
end ; End of program

41. Nadim Ahmed
Machine Code

42. Nadim Ahmed
Memory Before Running

43. Nadim Ahmed
Memory After Running

44. Nadim Ahmed
High Level Languages
• In order to make programming easier,
we use a high level language.
• When we use a high level language, we
need to convert it to machine code.
– This is called compilingcompilingcompilingcompiling.
– We use a compilercompilercompilercompiler to compile the sourcesourcesourcesource
codecodecodecode into machine code.
– Source code is our original high level code.

45. Nadim Ahmed
Multiplying in High Level
• You saw just how much effort was
required to multiply 3 by 2 in low level.
• In a high level language, we can just do
the following:
3*2

46. Nadim Ahmed
Syntax
• Syntax deals with the grammar of the
language.
– So, if you are speaking English, and say:
Cat ball hit.
– You have a syntax error.
•The cat hit the ball.
• The compiler will tell you about syntax
errors.

47. Nadim Ahmed
Semantic
• However, if your grammar is correct, but
the meaning is wrong, then you have a
semantic error.
The cat cooked some dolma.
• The grammar is correct, but I very much
doubt that a cat can actually cook dolma.

48. Nadim Ahmed
Semantic
• Let’s say you wrote down that the area
of a triangle is worked out by the
following equation:
length of base * height of triangle
• You have a semantic error.
• The compiler will not tell you that you
have a mistake in the equation.

49. Nadim Ahmed
C
• We will be using C as our high level
programming language.
• I have chosen ANSI C as it is a well
known standard that can be used by
most C compilers for different operating
systems.
• It is used widely by programmers and
academics in systems and graphics
programming.

50. Nadim Ahmed
In Summary
• We have seen
– What is a computer and programming.
– The basics of what is an algorithm.
– How programming is a form of recipe.
– Different levels of languages.
– Syntax and Semantics.