Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
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April 12, 2020

What is Computer Science?
• Not math
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April 12, 2020

What is Computer Science?
• Not “just” programming
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April 12, 2020

What is Computer Science?
• Computers are only tools
“Computer science is no more about computers than astronomy is about telescopes.”
- Dijkstra
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April 12, 2020

What is Computer Science?
• Computer Science = computational problem solving
• What is computation?
• Any calculation that follows a well-defined model (e.g., algorithm)
• To be solved computationally, a problem needs:
• Representation of all aspects of problem
• Algorithm that solves problem based on representation
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April 12, 2020

What is Computer Science
• Example problem: man, cabbage, goat, wolf
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April 12, 2020

• Only one can cross at a time
• Cabbage cannot be left alone with goat
• Goat cannot be left alone with wolf
• How to solve this?
• Information must be abstracted. e.g., { M = E, C = E, G = E, W = E }
• Algorithm- e.g., “brute force” vs. “search”
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April 12, 2020

What is Computer Science?
• There are limits to computation
• E.g., Traveling Salesman Problem
• Find shortest possible route of travel between set of cities
• “Brute force” approach (try all possible routes)
• 10 cities => 10! = ~3.5 million routes
• 20 cities => 20! = ~2.5 x 10 18 routes (2.5 quintillion!!)
• If computer could estimate 1,000,000 routes per second,
• It would take ~77,000 years to compute solution for 20 cities!!
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April 12, 2020

Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
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April 12, 2020

Algorithms
Algorithm- finite number of clearly described, unambiguous, “doable” steps that can be systematically followed to produce a desired result for given input in a finite amount of time.
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April 12, 2020

Algorithms
• Solve general problems
• E.g., algorithm to sort a list of numbers
• (should work for all lists of numbers)
• Computer is only as smart as the algorithm chosen
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April 12, 2020

Algorithms
• Computer are fast and don’t make errors
• Great for algorithms!!
• Errors are human caused!!
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April 12, 2020

Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
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April 12, 2020

Hardware
• Physical components of a computer
• Fundamental components:
• CPU
• main memory
• secondary memory
• input / output devices
• buses
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April 12, 2020

CPU – Central Processing Unit
• “Brain” of computer
• Uses digital logic to interpret and execute instructions
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April 12, 2020

Main Memory
• Where executing programs reside
• CPU accesses directly
• Fast
• Volatile (data lost on power cycle)
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April 12, 2020

Secondary Memory
• Large, persistent storage
• Slower than main memory
• Non-volatile (data persists on power cycle)
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April 12, 2020

Input / Output Devices
• Keyboard
• Mouse
• Monitor
• Printer
• etc.
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April 12, 2020

Buses
• Connect everything together
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April 12, 2020

Operating System
• Software that manages and interacts with hardware resources
• Acts as “middle man” between hardware and applications
• Also known as system software
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April 12, 2020

Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
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April 12, 2020

Software
• Set of instructions, data, and documentations that can be executed by a computer
• Application software fulfills a user’s needs
• Different from system software
• E.g., iTunes, iMovie, etc.
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April 12, 2020

Syntax vs. Semantics
• Syntax – set of characters and acceptable arrangements
• Semantics – meaning associated with each syntactically correct sequence of characters
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April 12, 2020

Syntax vs. Semantics
• Syntax errors
• Caused by invalid syntax
• E.g., prnt instead of print
• Semantic (logic) errors
• Errors in program logic
• Computers do not understand what program is meant to do
• Only follow instructions
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April 12, 2020

Program Translation
• Translates human-readable source code into machine code
• Instructions in 1s and 0s
• Most programs written in a high-level language
• E.g., Python, C++, Java, Ruby, etc.
• High-level language translated into machine code via:
• Compiler
• Interpreter
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April 12, 2020

Compiler vs. Interpreter
• Compiler is translator program
• Translates source code into machine code for CPU
• Interpreter
• Executes program instructions in place of (“on top of”) CPU
• “Interactive” mode
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April 12, 2020

Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
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April 12, 2020

Computational Problem Solving
• Four main steps:
1) Analyze
2) Design
3) Implement
4) Test
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April 12, 2020

Computational Problem Solving
• Four main steps:
1) Analyze – understand problem
2) Design
3) Implement
4) Test
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April 12, 2020

Computational Problem Solving
• Four main steps:
1) Analyze
2) Design – determine abstraction and algorithm
3) Implement
4) Test
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April 12, 2020

Computational Problem Solving
• Four main steps:
1) Analyze
2) Design
3) Implement – write code
4) Test
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April 12, 2020

Computational Problem Solving
• Four main steps:
1) Analyze
2) Design
3) Implement
4) Test – validate and verify code solves problem
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April 12, 2020

Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
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April 12, 2020

Python
• Invested by Guido van Rossum in early 1990s
• Simple syntax
• Easy to read
• Very powerful
• Used by YouTube, Google, Yahoo, NASA, etc.
• Free
• Has many built-in modules
• e.g., import math
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April 12, 2020

Python Basics
• Variables
• Arithmetic operators
• Input and output
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April 12, 2020

Variables
• A name that is assigned to a value, e.g., n = 5
(variable n assigned to value 5)
• Variables can be used and reassigned, e.g.,
• n + 20 = ?
• n = 10
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April 12, 2020

Arithmetic Operators
*
/
-
+ (addition)
(subtraction)
(multiplication)
(division)
2 + 5
2 - 5
2 * 5
2 / 5
** (exponentiation) 2**5
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April 12, 2020

Input and Output (using Python 2.7) print( value )
• Python function to write output (i.e., value) to the terminal
• value can be
• literal (e.g., 10, 44/2, “Hello”)
• Variable (e.g., name)
E.g., print(‘hello class!!!’)
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April 12, 2020

Input and Output (using Python 2.7) retval = raw_input( prompt )
• Python function to read input from the user
• Value entered stored in retval
• prompt is message displayed to user..
E.g., name = raw_input(“what is your name? “);
NOTE: The book uses Python 3.0, which is simply input()
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April 12, 2020

Today’s Schedule
• What is Computer Science?
• Algorithms
• Hardware
• Software
• Computational Problem Solving
• Python
• Live Coding
40
April 12, 2020

Live Coding
• Variables
• Arithmetic operators
• Input and output
• Common errors
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April 12, 2020