Prerequisites: Control Systems Overview

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Lesson 1: Getting Started

If you want to tell a computer to do something, you have to communicate with the computer in a programming language. When we say language, we mean it. A language has words and grammar and everything else, just like French.

Computers, despite what you may think, are dumb. They do only exactly what you tell them to, and don't guess or interpret. If say to your Mom or Dad "Hey, can you bring me that thing?", there's a (slim) chance they may bring you the right "thing". A computer wont. Ever. Just a cold, unfeeling "ERROR". A programming language is very precise, and to tell a computer what you want, you have to be precise too. In this training session, we'll introduce programming to you, and make some things work. You know, those things.

Hang on, it gets harder from here.

(A quick note...If you know all this already and are getting bored...CONGRATULATIONS! Here's a ​link to some cute corgi puppy videos as your reward. Then, come back and dive into a later section. This is all self-paced.)

We'll be starting with a programming language called ​Python, specifically Python 3. There are a lot of programming languages. Some are created because they're better for solving certain problems, others because people are bored and want to try something new. Python has been around for a while, and its pretty popular because its easy to use. The team uses Java to control the robot but that language is a little trickier. We'll get to that one later once you get a handle on the basics.

Python, like every programming language, has a structure. Here are the big parts:

• Variables: Things you assign to and read from. Like in Algebra. A="Dump Truck" sets the variable A to the string "Dump Truck". They're basically the nouns.
• Functions: These do things. They take nouns as arguments, do something, and can return nouns. In redCar = paintCarRed(blueCar), paintCarRed is a function. They're the verbs, they do things, and they take variables and return variables.
• Control Structures: These are instructions like IF this is true THEN do that…. These are like grammar rules, like use active voice, or use punctuation.
• Libraries: A lot of other people have written functions to do things. A lot of things. When these things are bundled together they're called libraries. You can tell a computer to use a library and save your self a lot of typing.

Much like in English, you blend all of these together to create stories, or programs. Both have a beginning middle and end. So lets write the first program that all programmers start with: "Hello World"

a="Hello World"
print(a)

This tells the computer to print, you guessed it, "Hello World"

Now you try it...Do the following:

1. Then highlight the code above, right click and click {{{Copy}}. This put the code on the clipboard so you can share it with another window.
2. Go ​here. This site is our code editor for training purposes, and its pretty cool. You can put code in the center section, and click Execute to run it. The lower window shows the results.
3. On that page, highlight all the code already in the center window.
4. Right click and pick {{{Paste}}}. This should replace everything in the window with the contents above.
5. Finally click {{{Execute}}} right above the center window to run the program.

(From now on, we'll call this step "Go ​here and run the code above". (Just come back to these steps if ever you forget how to do that).

After a bit, you'll be rewarded with the following message in the bottom window:

Hello World!

The program told the computer to print the value of variable a on the screen.

And, boom, now you're a programmer. The rest of learning how to code is just more details. This is the end of Lesson 1.

Lesson 2: Making decisions

In lesson 1, we had you create a program, "Hello World". Now, "Hello World" is not too exciting if you want to program robots, but its an important first step. We showed you how to run a function (or verb) print, which does something (show on the screen the value of its argument a, where a is assigned the value "Hello World".

If you want to do more, we need to introduce control structures. Take the program below.

location = 'HERE'
print("Welcome to our store\n")
if location == 'HERE':
   print("We're here! Come on in\n")
   print("Our ours are 11:00am-11:52am\n")
else:
   print("Go away, we're out eating tacos\n")
print("Hope you had a good time")

This program uses a IF-THEN-ELSE statement to tell the computer to make a decision in your program, and you'll use them all the time. Go ​here and run the code above. It should print:

Welcome to our store
                                                                                                                                                                                                                                  
We're here! Come on in
                                                                                                                                                                                                                                
Our ours are 11:00am-11:52am 
                                                                                                                                                                                                                         
Hope you had a good time                                                                                                                                                                                                                                

Three things to note about this program:

1. The double equals in location=='HERE' on the first line. It is called an expression. In this case it is an equals expression (other kinds of comparisons in python are listed here) . It returns True when the condition evaluates to True, otherwise its False. Note on that line the word 'HERE' is in quotes. That's to indicate its a string (a text value) not some variable (which doesn't exist). If you used = instead of == it wouldn't work as you expected because it would be a variable assignment. If a IF-THEN statement ever behaves in an unexpected way, check for this problem first, its a common error.
2. Spacing and indents are important in Python. the line "We're here..." and the line below it are indented to indicate they are part of a statement block that runs when the condition evaluates to True. The second block on the else is run when the condition to False, and only contains one line. If you want to do stuff outside of the IF-THEN, don't indent it like the first and last print statements.
3. You'll see that a few of the print statements end with a {{
   n}}. This is called a escape sequence, and its shorthand for a newline. When the computer sees it in a print statement, it will add an extra line to the output. See here for other escape sequences you can add.

Now, in the editor change the condition to location=='Poughkeepsie, NY' and run it again. What happens? It should print "Go away, we're out eating tacos". Why? If I was in Poughkeepsie, I'd be out eating tacos too. Yummmm, tacos.

If you're writing your own code, you want to the skip the else, just omit the word else: and the indented block below it. For example:

medianSalary=98260 #Median annual salary of a software engineer in the US 
salary=90000
if salary > medianSalary:
   print("Whohoo! Dinner's on you!")

Go ​here and run the code above. It should print:

Yep, nothing was output. Nada. In this case, we used variables which were numbers, and a greater-than expression to compare them. Since the condition was False, nothing was printed.

Here's a couple other control structures that you should know

For Loop: This one repeats over a variable. It's good for counting try running this one:;

For (Potato

While: The more charming cousin of the for loop, this one repeats

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