1. CSC 241: Introduction to Computer Science I
Class session 1:
An introduction to computer science and Python

2. An overview of today Course overview and logistics
An overview of computer science
A brief introduction to Python

3. Course overview and logistics
Instructor: Joseph (Yosef) Mendelsohn
Discussion of the syllabus
Course web site:
Course calendar
Textbook
Grading policy

4. Course overview and logistics
Other course issues
Office hours
Lab sessions
Mondays, 11:50-1:20, Same classroom as lecture
Teaching assistant: Wenwen Zhang
Attendance is mandatory
CodeLab
You will be using it during most of your lectures, labs, and assignments
See the information sheet under 'Resources' on the course web page
Course web sites
D2L: turn in assignments and labs here
Contains notes, code examples, links to assignments, labs
Other resources

5. An overview of today Course overview and logistics
An overview of computer science
A brief introduction to Python

6. Who is in this class? This class is for developers.
What majors are included?
Computer science
Computer game development
Gameplay programmers
Systems programmers
Information assurance and security engineering
Math & CS

7. What are the commonalities?
Each major requires understanding the basics of computer science
Software
Hardware
Problem solving in technical context
What is computer science?
The development and improvement of applications for computer systems
To do this, we need to know how to:
Solve problems
Program computers
Understand how to use computer systems

8. What is computer science?
Solving problems (in a broad sense) and developing techniques and technologies for solving problems
Problem solutions are represented by step-by-step instructions on how to solve the problem
Computer systems can be used to automate the execution of the instructions and accelerate the problem solving
Programming is fundamental to computer science

9. Specific problems Develop realistic computer games
Search for patterns in a text document or image
Efficiently send audio/video streams through the Internet
Search for a document on the web
Solve a scientific problem (in biology, chemistry, physics, mathematics, etc.)
Encrypt/decrypt credit card information
Break encrypted information
Aggregate information from company financial statements to create a market analysis
Develop personalized radio stations
Create a spam list

10. Focus problem: create a spam list
Suppose we want to create a CDM spam list and sell it
A CDM spam list is a list of addresses of faculty/staff/students at DePaul CDM
How do you solve this problem?
Where can be find addresses of CDM staff and faculty?
How do we go about collecting them and storing them in a file?
Doing this by hand is very tedious
We want to automate the process
How do we describe the step-by-step instructions on how to collect the addresses?

11. Algorithms
We describe the step-by-step instructions needed to solve a problem as an algorithm
An algorithm is an ordered sequence of unambiguous instructions that when executed on a specific input produces the desired output
Of course the algorithm needs to be correct, and the more theoretical areas of computer science concern themselves with how to do this
To specify an algorithm you need to make the problem statement as precise as possible
A first step: Clearly specify the input and output

12. Spam list algorithm Input: DePaul CDM web site URL
Output: A list of addresses appearing on web pages belonging to the DePaul CDM web site
The algorithm (assuming _list is initially empty):
Spam_List_Algorithm(URL)
Download URL file from the web
Search the URL file for addresses and add them to the list
Search the URL file for URL hyperlinks and call the Spam_List_Algorithm on each

13. From algorithms to programs
A person could execute the spam list algorithm
Algorithms are best automated
Computing and algorithms have existed for thousands of years but the creation of computers has accelerated growth in the field
To automate an algorithm we need to write a program
A program is an algorithm written in a form that the computer can understand
An algorithm versus a program:
Both are precise step-by-step descriptions for solving a problem
An algorithm is written for humans and is computer system independent
A program uses a language humans can understand but can be executed on a computer system, so that it is dependent on the system, including the hardware, OS, programming language, etc.

14. Programming languages
Some programming languages
Some taught at CDM: Python, Java, C++, C#, Javascript, Ruby
Two sample “hello world” programs:
Java:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello world"); }
Python:
print ("Hello world")

15. Programming languages
There is no single programming language that is best for all tasks
If there were, the others wouldn’t continue to exist!
Each language has its strengths and weaknesses
The advantage of Python
It has simple syntax
It is easier to learn than other languages
It allows very fast development
For example, Google encourages its software developers to build prototypes for new applications in Python
An application programming interface (API) is a source code interface that a computer application, operating system, or library provides to support requests for services to be made of it by a computer program

16. An overview of today Course overview and logistics
An overview of computer science
A brief introduction to Python

17. The focus of our Course
We will learn the following things in this class:
The Python programming language
The Python API
How to use Python to solve basic computer science problems (and with it)
An overview of the problems that interest computer scientists
Next we need to understand how to get started writing Python programs

18. Basic system setup
Download the Python software from: (Use version or greater)
Create a csc241 directory to store your programs (and subdirectories as needed)
Open a command-line window
Ask if you don’t know how to find it on your system
Open IDLE, i.e. the Python Integrated DeveLopment Environment