Lecture notes on first topic in CSC1015 (Basics of Programming). Combines notes from lectures and recommended textbook (Python Programming: An Introduction to Computer Science (2nd edition) by John Zelle).
Lesson 1: Hello World
Program:
Set of instructions given to computer corresponding to an algorithm to solve a problem.
Programming (writing programs) in a programming language (e.g. Python)
Input Process internally Output (like a mathematical function, diff input => diff output)
Python:
Programs stored in text files.
Program = set of instructions interpreted by python interpreter executed (user command)
Python interpreter: (python3)
o Instructions run one at a time.
o Executes each instruction and prompts user for next, exit() to end
o Useful for testing code and exploring functions/modules
o Note: always save your python files .py
Usually done through Integrated Development Environment (IDE)
o Graphical interface (like word)
Structure:
# what the program does
# author of program
# date
Python Instruction 1
Python Instruction 2
print(“Hello World”) :
print = name of function, “Hello World” = argument/value input into function
Lesson 2: Numbers and Variables
Program Syntax & Style:
Every statement (instruction) on new line
Case-sensitive
# = comments to describe code
o Brief description of code/of each function/explanation of non-obvious parts of code,
author, date
Syntax & Logic errors:
o Syntax error = program doesn’t conform to structure required => program won’t run
o Logic error = program runs but doesn’t work as expected (always test!!)
Escape Sequences: (useful, keep them on hand)
o Special characters that can’t be represented easily:
o \a - bell (beep)
o \b – backspace
o \n – newline
o \t – tab
o \’ – single quote
, o \” – double quote
o \\ - \ character
Numeric Data Types:
- 2 primitive types of numbers:
o Integer = whole number, no fraction
o Floating point number = has fractional part, stores only as APPROXIMATION to real
number, there is a limit to accuracy of stored values (e.g. 10/3)
- Integers:
o Literals
Actual data values written into program.
Numeric literals can be output like text, e.g.:
print(12) 12
print(12+13) 25
o Expressions
+, -, /, *, % (mod)
// (integer division – always goes towards negative infinitiy)
a**b (a to the power of b)
Precedence of operation = BODMAS (1st = (), 2nd = * and /, 3rd = + and -)
Modulus (%)
- aka integer remainder operator
- a % b = remainder of a dividend by b
- e.g. 18 % 5 = 3 (closest multiple of 5 is 15, therefore 18-15 = 3)
- e.g. 5 % 2 = 1 (closest multiple of 2 is 4, therefore 5-4 = 1)
Identifiers:
print = identifier (reserved – has a particular meaning)
Used to name parts of program.
o Start with _ or letter, followed by _, letter, or digit e.g. hello_world
Reserved words = if, for, else (they have special meanings, therefore cannot be used for other
purposes)
Variables:
Sections of memory where data can be stored.
Most variables have identifiers e.g. a_value
Defined by assigning initial value to them e.g. a_value = 10
Assignment and Output (I/O):
LHS is the variable, RHS is the expression e.g. b = a + 5
Output values are like literals (can do both on one line) e.g. print(“The value is “, a)
Lesson 3: Input and Output
Output: print
print = built-in function with precise set of rules for how it works.
Displays value of each expression, separated by blank spaced followed by carriage return.
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