Unit #2-03

Learning Outcome

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

• understand what a constant is and how to use one

• understand what a flowchart is and how to create one

Review

• review variables

Lesson

• read Flowcharts, from textbook Computer Based Problem Solving

• read Constants, from textbook Computer Based Problem Solving

• go over what a Flowchart is

  • we use square line connectors

  • different shapes have different meanings

  • arrows always point down

  • normally left black & white

• go over how to create one using draw.io

  • yes, same extension as for Top-Down Designs

  • once again, to get your Flowchart into your Google Doc ALWAYS export it as a PNG file

    • the reason is that the resolution of the diagram is kept and even if you need to shrink it to fit nicely on the page, I can zoom in and still see all the text

    • File, Export As, PNG...

    • then insert it into your Google Doc

      • Insert, Image

    • ensure you then center, size and crop the image appropriately so it fits nicely on one (1) page

    • NEVER take a screenshot from Draw.io and paste that in!

• go over what a constant is

  • we will always use this rule:

    • uppercase with words separated by underscores as necessary to improve readability

    • also, constants will always be created in a separate module

      • go over how to create a module, it is just a separate python file

    • ex: MONTHS_IN_YEAR, SECONDS_IN_HOURS, HST

  • note: in python even when you declare a constant, someone could still change it; this is not true in all languages; in C and swift for example if you declare a constant it can never be changed

    • to get around this we normally create a new python file (usually called constants) and place our constants in there and then "import" that file

Activity

• see Mars program (see source code below: ↓)

  • ensure you click on "Show Files" to see the mars.py file, if you can not see the file explorer

    • once there, ensure you click on "Files" to see the constants.py file as well

Daily Assignment

• create a program that calculates the circumference of a circle using τ (tau), with radius entered by user and having 3 decimal places (see terminal below: ↓)

  • C = τr, τ ~= 6.28 

  • dimensions entered by user

  • come up with three (3) test case, BEFORE YOU WRITE THE CODE to ensure you know what the answer should be BEFORE you start coding

    • note, you can not use my test cases!

    • then check to ensure your answers are correct!

• you will have to create a constants.py file to hold the value of tau

  • remember, TAU in your constants file should be in all CAPS

Extra

• create the same above program in C

• constants in C can be done 2 different ways:

  • #define vs const

    • we will just use const, so that it is not global and can be type checked!

• constant example in C:

  • note: constants in C are NOT declared in a separate file, they are declared above variables

  • const int  LENGTH = 10;