Program Design and Development

Designing a Program

• Programs must be designed before creation
• The program development cycle encompasses design, coding, syntax correction, testing, and debugging.
• Design is the most important part
• Understand the task by working with the customer to establish project requirements
• Determine the necessary steps; break down the task and create an algorithm.
• An algorithm consists of well-defined logical steps to perform a task

Pseudocode

• Pseudocode is informal language that has no syntax rules.
• Pseudocode is not compiled or executed.
• Pseudocode helps to create a model program, and can be translated into code for any programming language

Flowcharts

• Flowcharts are diagrams which graphically represent program steps
• Ovals: Terminal symbols.
• Parallelograms: Input and output symbols.
• Rectangles: Processing symbols
• Arrows: Represent the program's flow

Input, Processing, and Output

• Computers generally follow a process including input, processing, and output
• Input is data received while the program runs
• Processing involves actions like mathematical calculations
• Output is the result of processing

Displaying output with print Function

• Functions are blocks of prewritten code performing specific operations
• The print function displays output on the screen
• Arguments represent the data passed and used in a function
• Statements execute sequentially, top to bottom in a program

Strings and String Literals

• Strings are character sequences used as data
• String literals appear directly in the code
• String literals are enclosed in single (') or double (") quotes
• Triple quotes (""" or ''') allow multi-line strings and inclusion of both types of quotes

Comments

• Comments are explanatory notes ignored by the Python interpreter
• They are intended for those reading the code
• Comments begin with a # character
• End-line comments appear at the end of a line of code, clarifying its purpose

Variables

• Variables are names representing values in computer memory
• Variables facilitates accessing and manipulating stored data
• They hold a reference values they represent
• Assignment statements create a variable and assign it data, such as: variable = expression
• The equal sign (=) is the assignment operator
• The variable receiving the value must be on the left side

Variable Naming Rules

• Variable names cannot match Python keywords, contain spaces
• Variable name must start with a letter or underscore
• Subsequent characters can be letters, digits, or underscores
• Variable names are case-sensitive
• Variable names should reflect the variable's use

Displaying Multiple Items with the print Function

• Python's print function can display multiple items
• Use commas to separate items when passing in as arguments
• Arguments are displayed in the order given
• Items are automatically separated by a space on screen

Variable Reassignment

• Variables can reference different values during runtime
• Garbage collection is the automatic removal of values no longer referenced
• A variable can refer to items of any data type
• Reassignment can change a variable's type.

Numeric Data Types, Literals, and the str Data Type

• Data types categorize values in memory
• int is for integers, float for real numbers, str for strings stored in memory
• Numeric literals are numbers written in a program
• Numbers are considered int by default unless a decimal point is present, in which case it's float
• Operations behave differently based on data type

Reading Input from the Keyboard

• Most programs require user input
• The built-in input function reads input from the keyboard as a string
• The format is: variable = input(prompt)
• Prompts usually instruct users to enter a value
• Programs do not automatically display a space after the prompt

Reading Numbers with the input Function

• The input function returns a string
• int(item) converts item to an integer
• float(item) converts item to a float
• Nested function calls follow the structure: function1(function2(argument))
• A float is the result of the operation if you include both int and float.
• Type conversion throws an exception if the item is not a valid numeric value

Performing Calculations

• Math expressions perform calculations and return values
• Math operators are tools (+, -, *, /, etc.) for performing calculations
• Operands surround the operators
• Variables can be used as operands
• The resulting value is typically assigned to a variable
• / operator performs floating point division
• // operator performs integer division
• Positive results are truncated, while negative results are rounded away from zero

Operator Precedence and Grouping with Parenthesis

• Python operator precedence in order:
  • Parentheses
  • Exponentiation (**)
  • Multiplication (*), Division (/ and //), Remainder (%)
  • Addition (+) and Subtraction (-)
• Higher-precedence operations are performed first
• Operators of the same precedence are executed from left to right

The Exponent Operator and the Remainder Operator

• The exponent operator (**) raises a number to a power
• X ** Y = X to the power of Y
• Remainder operator (%) does division and provides the remainder
• aka modulus operator
• E.g., 4%2=0, 5%2=1
• The remainder operator is also used to convert times or distances, and to detect odd or even numbers

Converting Math Formulas to Programming Statements

• Operators are a requirement for any mathematical operation
• When converting to programming statements, multiplication operators and parentheses may be necessary

Mixed-Type Expressions and Data Type Conversion

• The data type depends on operands
• Two int values lead to an int result
• Two float values lead to a float result
• Use of int and float results in a float
• Converting float to int truncates the fractional part

Breaking Long Statements into Multiple Lines

• Long statements are difficult to read on screen and do not print without cutting off
• The multiline continuation character () breaks a statement into multiple lines
• Portions in parentheses can be broken without a continuation character

String Concatenation

• To append one string to the end of another string
• The + operator concatenates strings
• String concatenation breaks up a long string literal

Implicit String Literal Concatenation

• Two or more adjacent string literals concatenate into one string

More About The print Function

• print function displays a line of output and adds a new line at the end
• A special argument end='delimiter' replaces the newline character with a delimiter
• By default the print function uses space as item separator
• sep = 'delimiter' replaces the space with a delimiter
• Special characters in string literals are preceded by a backslash ()
• Newline (\n) and horizontal tab (\t) are treated as commands in strings

Displaying Formatted Output with F-strings

• An f-string is a string literal prefixed with f
• F-strings support placeholders for variables
• Placeholders can also be expressions that are evaluated
• Format specifiers can be used with placeholders: f'{num:.2f}'
• .2f rounds the value to 2 decimal places and displays the number as a floating-point
• Minimum field width can be specified: f'The number is {num:12,.2f}'
• Values can be aligned within a field
• <: left alignment
• >: right alignment
• ^: center alignment
• Follow this format to use multiple designators in a format specifier: [alignment][width][,][.precision][type]

Magic Numbers

• Magic numbers are unexplained numeric values in a program's code
• Magic numbers make it difficult to determine the numbers purpose
• Magic number makes it difficult to change if used in multiple places
• Magic numbers can introduce risks of typographical errors

Named Constants

• Named constants are recommended instead of magic numbers.
• Named constants represent values that don't change during program execution
• Named constants enhance code self-documentation, maintenance, and error prevention

Introduction to Turtle Graphics

• Python's turtle graphics system features a small cursor, known as a turtle.
• Users can move the turtle around the screen, drawing lines and shapes using Python statements.
• To use the turtle graphics system, import the turtle module - import turtle.

Turtle Methods

• turtle.forward(n): moves the turtle forward n pixels.
• turtle.right(angle): turns the turtle right by angle degrees.
• turtle.left(angle): Turns the turtle left by angle degrees.
• turtle.setheading(angle): sets the turtle's heading to a specific angle
• turtle.penup(): Raises the pen
• turtle.pendown(): Lowers the pen
• turtle.circle(radius): Draws a circle with a specified radius
• turtle.dot(): draws a simple dot at the turtle's current location.
• turtle.pensize(width): Change the width of the turtle's pen, in pixels
• turtle.pencolor(color): Change the turtle's drawing color
• turtle.bgcolor(color): set the window's background color.
• turtle.setup(width,height): set the size of the turtle's window, in pixels.
• turtle.reset(): Erases all drawings, resets drawing color to black, and resets the turtle to original position
• turtle.clear(): Erases drawings but does NOT change turtle's position or drawing color
• turtle.clearscreen(): Erases drawings, resets drawing color to black, resets turtle position, and the window background color to white
• turtle.goto(x, y): Move the turtle to a specific location.
• turtle.pos(): Displays the turtle's current X,Y coordinates.
• turtle.xcor(): Displays the turtle's current X coordinate
• turtle.ycor(): Displays the turtle's current Y coordinate
• turtle.speed(speed): Change the speed at which the turtle moves, argument is a number in the range of 0 through 10
• turtle.hideturtle(): hideturtle
• turtle.showturtle(): display the turtle.
• turtle.write(text): display text in the turtle's graphics window
• turtle.begin_fill(): Before drawing the shape
• turtle.end_fill(): Shape will be filled with the current fill color
• turtle.numinput(): Prompt a window for numerical input
• turtle.textinput(): Prompt a window for text input
• turtle.done(): Keeps the Graphics Window Open

Attributes of the Turtle Graphics Window

• Cartesian Coordinates are implemented
• Pen up and Down function
• Drawing Circles function
• Drawing Dots function
• The pen size and drawing colors can be adjusted
• The program can implement Text
• The turtle's window can implement shape filling