Unit2-01: Top-Down Design, Variables & User Input

Learning Outcome

At the end of this lesson, you will be able to:

• A1.1 use constants and variables, including integers, floating points, strings, and Boolean values, correctly in computer programs; 

• A1.3 use assignment statements correctly with both arithmetic and string expressions in computer programs; 

• A1.6 write programs that declare, initialize, modify, and access one-dimensional arrays.

• B2.4 represent the structure and components of a program using industry-standard programming tools (e.g., structure chart, flow chart, UML [Unified Modeling Language], data flow diagram, pseudocode); 

• B4.1 describe the phases (i.e., problem definition, analysis, design, writing code, testing, implementation, maintenance), milestones (e.g., date of completion of program specification), and products (e.g., specification, flow chart, program, documentation, bug reports) of a software development life cycle; 

• understand what a variable is and how to use one

• create an application that accepts input and saves it to a variable

• understand what a top-down design is and how to create one

Quiz Questions

With a pencil and paper, answer the following questions:

1. What is "import math" used for in Python? What is its equivalent in C++?

2. Declare 2 variables, length with a value of 6cm and width with a value of 4cm.

3. Write the code that creates 2 variables, area and perimeter, and uses length and width to calculate the area and perimeter of a rectangle.

Review

• 6-step process

• modules in Python

  • import math 

• libraries in C++

  • #include <cmath>

 Variables, Assignment Statements & Data Types

• what is a variable?

  • it is  a container that stores a value that can change

  • in Python, we will use the following naming convention:

    • all lowercase with words separated by underscores

    • i.e. area_of_rectangle, time_of_day, number_of_students

• what is an assignment statement?

  • used to assign a value to a variable

  • we  always use a single "=" to do this!

  • for example:

    • score = 0 means score has the value 0

    • first_name = "Jolie" means the variable first_name is assigned "Jolie"

    • message_sent =true means that the variable message_sent is set to true

• go over different data types in Python

  • #!/usr/bin/python3
    counter = 100  # An integer assignment
    miles   = 1000.0  # A floating point
    name    = "John Whyte"  # A string
    student_passed = true  # A boolean

print (counter)
print (miles)
print (name)
print (student_passed)

• what is a string in programming?

  • a sequence of characters in between double quotes

  • here are some string examples:

    • "This is a string!"

    • "K1S 5P4"

    • "98"

Type Casting & Getting Input from the User in Python 

• how do we get input from a user?

  • user input will ALWAYS be in the form of a "string" (a sequence of characters)

  • if you ask the user to enter a number, that number will first be in the form of a string

  • use type casting (or just casting) to convert the string to an int

    • type casting is used to convert one data type to another

      • for example, the following converts the string "5" to the integer 5:

      • score = int("5")

  • # just start using a variable right away in Python
    length = int(input("Enter length of the rectangle (mm): "))

Activity

• in groups of 2, do the following on the board for today's daily assignment:

  • Top-Down Design

Daily Assignment

• complete the Daily Assignment section in Hãpara Workspace for this day

  • if Hãpara is not working, make a copy of this document

  • move it to your IMH-ICS folder for this course

Extra

• create the above program in C++

  • note the variable naming convention for C++:

    • lowercase to start, then uppercase, with words NOT separated to improve readability

    • for example:

      • float areaOfRectangle =94.78;

      • int numberOfStudents = 30;

      • std::string name = "Bob";

Type Casting & Getting Input from the User in C++

• in C++ the user input does not necessarily have to be converted because it is not always in the form of a string like Python

• // declare the variable first in C++
  int length;
  ...
  // then you can use it!
  std::cout << "Enter length of the rectangle (mm): "<< std::endl;
  std::cin >> length;