Introduction to Computer Programming

Abstract¶

By the end of this material, readers will understand the intimate relationship between computers and programming, and appreciate the evolutions and motivations of programming languages. They will learn about basic computer architecture, binary data representation, and the structure of a Python program.

from __init__ import install_dependencies

await install_dependencies()

# Set LLM alias
%load_ext jupyter_ai
%ai update chatgpt dive:chat

Computer¶

What is a computer?¶

A calculator that is bigger and more advanced?

Calculator app — Figure 1:A calculator on a computer.

If so, is abacus the first computer ever invented?

Is your smartphone a computer?

Run the following cell to ask AI how to defines a computer:^[2]

%%ai chatgpt -f text
What defines a computer? Explain in one line.

What is the architecture of a computer?¶

A computer contains three main hardware components:

Input device
Processing unit
Output device

Peripherals¶

Input and output devices connected to a computer are called peripherals.
They allow users to interact with the computer in different ways.

Solution to Exercise 1 #

3D printer available at CityU

%%ai chatgpt -f text
Summarize what an output device of a computer is and explain briefly why 
a monitor and a speaker are examples?

Solution to Exercise 2 #

3D scanner available at CityU

%%ai chatgpt -f text
Summarize what an input device of a computer is and explain briefly why 
a keyboard and a mouse are examples?

Solution to Exercise 3 #

Hard disk
CD/DVD Rom (writable)
Touch screen

%%ai chatgpt -f text
Explain in one line why a headset is both an input device and an output device at the same time.

Central Processing Unit¶

The brain of a computer is its processor or the Central Procesisng Unit (CPU). As shown in Figure 4, it is located on the motherboard and connected to different peripherals using different connectors.

Two important components in the CPU are:

Arithmetic and Logic Unit (ALU): Performs arithmetics like a calculator (but for binary numbers)
Control Unit (CU): Directs the operations of the processor in executing a program.

To visualize how CPU works, run the CPU Simulator below.

Note that all values are zeros in the RAM (Random Acess Memory) initially.
Under Settings, click Examples $\to$ Add two numbers. Observe that the values in the RAM have changed.
Click Run at the bottom right-hand corner.

Programming¶

What is programming?¶

Solution to Exercise 4 #

The first six lines of binary sequences in the RAM. The last line Ends the program.

%%ai chatgpt
Summarize what a machine language is and give an example of a program in machine language.

The CPU is capable of carrying out

a set of instructions such as Add, Subtract, Store, etc.,
for some numbers stored in the RAM.

Both the instructions and the numbers are represented as binary sequences.

Why computer uses binary representation?¶

Two programmers operating ENIAC. — Figure 5:Programmers controlling the switches of ENIAC.

Notebook Cell

### BEGIN SOLUTION
2 ** 10 # because there are that many binary sequences of length 10.
### END SOLUTION

%%ai chatgpt -f text
Explain the multiplication rule in combinatorics.

There are International Standards for representing characters:

ASCII (American Standard Code for Information Interchange) maps English letters and some other symbols to 8-bits (8 binary digits, also called a byte). E.g., A maps to 01000001.
Unicode can also represent characters in different languages such as Chinese, Japanese...etc.

There are also additional standards to represent numbers other than non-negative integers:

2’s complement format for negative integers (e.g. -123)
IEEE floating point format for floating point numbers such as $1.23 \times 10^{-4}$ .

Generations of programming languages¶

Are we going to start with machine language? Start with learning 2’s complement and the binary codes for different instructions?

No. Programmers do not write machine codes directly because it is too hard to think in binary representations.

Instead, programmers write human-readable mnemonics such as ADD, SUB, ...
This is called the assembly language. An example is shown in Figure 6.

%%ai chatgpt -f text
What is the assembly language most commonly used by programmers and what is its
main application?

Are you going to learn an assembly language?

Both machine language and assembly language are low-level languages which are

difficult to write for complicated tasks (requiring many lines of code), and
platform-specific, i.e.,
- the sets of instructions and their binary codes can be different for different types of CPUs, and
- different operating systems use different assembly languages/styles.

High-level Language¶

What is a high-level language?

The art of programming

Programmer nowadays write in human-readable languages such as

C/C++
Java
JavaScript/Typescript
Pascal
Basic
HTML
PHP
Python
...

called high-level languages.

A program written in a high-level language gets converted automatically to a low-level machine code for the desired platform.
This abstracts away low-level details that can be handled by the computer automatically.

For instance, a programmer needs not care about where a value should be physically stored if the computer can find a free location automatically to store the value.

Different high-level languages can have different implementations of the conversion processes:

Compilation means converting a program well before executing the program.
E.g., C++ and Java programs are compiled.
Interpretation means converting a program on-the-fly during the execution of a program.
E.g., JavaScript and Python programs are often interpreted.

%%ai chatgpt -f text
Explain in one or two paragraphs whether Python is really an interpreted language, given that it also has a compiler and, recently, a JIT compiler, and it can be run as a script like a scripting language.

What programming language will you learn?

You will learn to program in Python, which is currently the most popular language according to the TIOBE (The Importance of Being Efficient) Programming Community Index.

We will cover

basic topics including values, variables, conditional, iterations, functions, composite data types,
advanced topics that touch on functional and object-oriented programming, and
engineering topics such as numerical methods, optimizations, and machine learning.

How does a Python program look like?

import datetime  # library to obtain current year

cohort = input("In which year did you join CityU? [e.g., 2020]")
year = datetime.datetime.now().year - int(cohort) + 1
print("So you are a year", year, "student.")

A Python program contains statements just like sentences in natural languages. E.g.,

cohort = input("In which year did you join CityU? ")

which obtains some information from user input.

For the purpose of computations, a statement often contains expressions that evaluate to certain values. E.g.,

input("In which year did you join CityU? ")

is an expression with the value equal to what you input to the prompt.
That value is then given the name cohort.

Expressions can be composed of the following objects:

Functions such as input, now, and int, etc., which are like math functions the return some values based on its arguments, if any.
Literals such as the string "In which year did you join CityU? " and the integer 1. They are values you type out literally.
Variables such as cohort and year, which are meaningful names to values.

To help others understand the code, there are also comments that start with #.
These are meant to explain the code to human but not to be executed by the computer.

Solution to Exercise 6

Programming using natural languages. A step towards this direction: ChatGPT for coding.
Write programs that people enjoy reading, like literate programming. A step towards this direction: nbdev.
Literate programming

%%ai chatgpt
What do you think the next generation programming should be?

Footnotes¶

Click me to see an answer.
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You can run a cell by selecting the cell and press Shift + Enter.
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To edit a markdown cell, double click the cell until you see a cursor. Run the cell to render the markdown code.
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The CPU simulator follows the von Neumann architecture, which realizes Turing’s conception of the stored-program computer, where program and data are stored in the same memory. This is in contrast to the Harvard architecture, which uses separate memories for program and data.
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References¶

Turing, A. M. (1937). On Computable Numbers, with an Application to the Entscheidungsproblem. Proceedings of the London Mathematical Society, s2-42(1), 230–265. 10.1112/plms/s2-42.1.230
von Neumann, J. (1993). First draft of a report on the EDVAC. IEEE Annals of the History of Computing, 15(4), 27–75. 10.1109/85.238389