Class Coding Lab: Introduction to Programming

The goals of this lab are to help you to understand:

1. How to turn in your lab and homework
2. the Jupyter programming environments
3. basic Python Syntax
4. variables and their use
5. how to sequence instructions together into a cohesive program
6. the input() function for input and print() function for output

Let's start with an example: Hello, world!

This program asks for your name as input, then says hello to you as output. Most often it's the first program you write when learning a new programming language.

TO RUN THIS CODE: Click in the cell below and click the run cell button.

NOTE: After the code executes, you will see a sequence number next to the code and output below the code itself. This is your indication the code in the cell has run. You must run all code cells in the notebook for full credit.

Believe it or not there's a lot going on in this simple two-line program, so let's break it down.

• The first line:
  • Asks you for input, prompting you with What is your Name?
  • It then stores your input in the variable your_name
• The second line:
  • prints out the following text: Hello there
  • then prints out the contents of the variable your_name

At this point you might have a few questions. What is a variable? Why do I need it? Why is this two lines? Etc... All will be revealed in time.

Variables

Variables are names in our code which store values. I think of variables as cardboard boxes. Boxes hold things. Variables hold things. The name of the variable is on the ouside of the box (that way you know which box it is), and value of the variable represents the contents of the box.

Variable Assignment

Assignment is an operation where we store data in our variable. It's like packing something up in the box.

In this example we assign the value "USA" to the variable country

Variable Access

What good is storing data if you cannot retrieve it? Lucky for us, retrieving the data in variable is as simple as calling its name:

At this point you might be thinking: Can I overwrite a variable? The answer, of course, is yes! Just re-assign it a different value:

You can also access a variable multiple times. Each time it simply gives you its value:

The Purpose Of Variables

Variables play an vital role in programming. Computer instructions have no memory of each other. That is one line of code has no idea what is happening in the other lines of code. The only way we can "connect" what happens from one line to the next is through variables.

For example, if we re-write the Hello, World program at the top of the page without variables, we get the following:

When you execute this program, notice there is no longer a connection between the input and the output. In fact, the input on line 1 doesn't matter because the output on line 2 doesn't know about it. It cannot because we never stored the results of the input into a variable!

1.1 Now Try this

Re-write the program above to input a name and then say hello there, name. It will need to store the first line in a variable so that it can be printed on the 2nd line.

What's in a name? Um, EVERYTHING

Computer code serves two equally important purposes:

1. To solve a problem (obviously)
2. To communicate how you solved problem to another person (hmmm... I didn't think of that!)

If our code does something useful, like land a rocket, predict the weather, or calculate month-end account balances then the chances are 100% certain that someone else will need to read and understand our code.

Therefore it's just as important we develop code that is easily understood by both the computer and our colleagues.

This starts with the names we choose for our variables. Consider the following program:

What do x and y represent? Is there a semantic (design) error in this program?

You might find it easy to figure out the answers to these questions, but consider this more human-friendly version:

Do the aptly-named variables make it easier to find the semantic errors in this second version?

1.2 Now Try This

Write a program to input your name and your age and the print name and age on a single line.

Example:

Enter your name: Mike
Enter your age: 25
Mike is 25

In the above example Mike was the entered name, and 25 was the entered age.

1.3 Now Try This:

Now try to write a program which asks for two separate inputs: your first name and your last name. The program should then output Hello with your first name and last name.

For example if you enter Mike for the first name and Fudge for the last name the program should output Hello Mike Fudge

HINTS

• Use appropriate variable names. If you need to create a two word variable name use an underscore in place of the space between the words. eg. two_words
• You will need a separate set of inputs for each name.

Variable Concatenation: Your First Operator

The + symbol is used to combine to variables containing text values together. Consider the following example:

1.4 Now Try This

Write a program to prompt for three colors as input, then outputs those three colors as a lis, informing me which one was the middle (2nd entered) color. For example if you were to enter red then green then blue the program would output: Your colors were: red, green, and blue. The middle was is green.

HINTS

• you'll need three variables one for each input
• you should try to make the program output like my example. This includes commas and the word and.
• name your variables appropriately!

F-Strings

In Python 3.7, f-strings were introduced to make it easier to format string literals in the print() statement.

Here's how it works:

• Put an f in front of the string literal
• Any variable you want to print enclose in {curly braces}
• At run-time the variable in {curly braces} is replaced with its value!

For example:

1.5 Now Try This

Re-write the last program (1.4) to print using f-strings!

Metacognition

Please answer the following questions. This should be a personal narrative, in your own voice. Answer the questions by double clicking on the question and placing your answer next to the Answer: prompt.

Questions

1. Record any questions you have about this lab that you would like to ask in recitation. It is expected you will have questions if you did not complete the code sections correctly. Learning how to articulate what you do not understand is an important skill of critical thinking.

Answer:

1. What was the most difficult aspect of completing this lab? Least difficult?

Answer:

1. What aspects of this lab do you find most valuable? Least valuable?

Answer:

1. Rate your comfort level with this week's material so far.

1 ==> I can do this on my own and explain how to do it.
2 ==> I can do this on my own without any help.
3 ==> I can do this with help or guidance from others. If you choose this level, please indicate HOW this person helped you.
4 ==> I don't understand this at all yet and need extra help. If you choose this please try to articulate that which you do not understand to the best of your ability.

Answer:

How Do I hand in my Work?

FIRST AND FOREMOST: Save Your work! Yes, it auto-saves, but you should get in the habit of saving before submitting. From the menu, choose File --> Save Notebook. Or you can use the shortcut keys CTRL+S

Handing in your Homework and Labs is easy! All you need to do is run the code cell below and follow the directions. This code sends your assignment to a private cloud where your instructor can download a copy of it at the time of submission.

Once the assignment is graded, you will see a grade and feedback / comments in Blackboard.