1. Benfeard Williams June 16th, 2016
How to Read Code
Benfeard Williams
June 16th, 2016
Learning the “grammar” of coding. Similar to a foreign language, reviewing the basics beneficial

2. Concepts You Will Learn
Programming
Skill, science, engineering, art, creativity
Problem-solving
How to solve problems using computer programming
Impact of computer science
Scale and automation
Foundation for future work
There are many different ways to use code to address a problem – learn a style and type that works best for you
Use code as a tool to help you avoid manual labor that would take you much longer

3. Things to know whenever you are reading code
Details to consider

4. Interpreted vs Compiled Code
Read and executed by another program on the target machine
Easy to implement
Compiled
Expressed specifically for the target machine
Faster performance
Important to know for sharing and running shared code. Python and R can be installed on a computer and used to run shared (interpreted) code. However, some programs have specified instructions for installation, indicating that the code behind that program are compiled for that machine

5. Computers Do What You Tell Them
They are fast but not smart
You need to plan exactly what the computer needs to do in order to solve a problem
YOU need to know how to solve the problem in order for the computer to carry out that task for you. Even if you couldn’t in your lifetime perform a certain analysis, you can tell the computer exactly how to do it.

6. Declarative Knowledge
Statements of fact
“A good health care plan improves the quality of medical care while saving money”
“y is the square root of x if and only if y*y = x”
Aka, if we want to know if y is the square root of x, we need to “fulfill” this statement. Aka, statement must be true

7. Imperative Knowledge How to accomplish something (recipe)
Start with a guess, g
If g*g is close enough to x, then g is a good approximation of the square root of x
Otherwise, create a new guess by averaging g and x/g.
Using this new guess, go back to step 2
Get close
Get closer (if g not close enough)
Check

8. What will you see in code?
What is in the code that you need to pay attention to in order to understand what it’s doing
What will you see in code?

9. Building Blocks Variables Data types Operators Functions (subroutines)
Name of a storage location
Assign a value to a variable
Data types
Various classifications of data
Operators
Arithmetic: + - * / % **
Functions (subroutines)
Sequence of instructions to perform a specific task
Variable – where you are storing data in order to use later, with specific name (not a physical location)

10. Variables Names are unique and can be abstract
What is
What is
Declare a variable and assign a value
Name and type
Examples: int age = 18;
age = 18
Example of assigning a name (age) to a piece of data (18)
Can explicitly state data type (int age) or sometimes the computer will infer the type (age) – see next

11. Data Types Int (integer) Float (floating-point number)
4, 13, -7
Float (floating-point number)
Work just like normal numbers
ans = 2 * (7 + 4) – 1
ans = 21
Example: if we set some variable (ans) to a mathematical statement, the computer can run the math and set this as the variable

12. Data Types Char (characters) Str (string) Arithmetic manipulation
“HELLO”, “Echo 123”
Arithmetic manipulation
phrase = “My name is ” + “Benfeard”
phrase = “My name is Benfeard”
Known that they are text because they are in quotes (so “3” can NOT be used as a number – has no numerical value)
Can use either single or double quotes, but must be consistent
Anything within the quotes are interpreted as a single unit (string) and can add these strings together
Now will form a new string

13. Data Types Arrays/List Manipulation Indexing elements
Collection of elements
[ 1, 2, 3, 4, 5] [ ‘A’, ‘B’, ‘C’, ‘D’, ‘E’ ]
Manipulation
myArray = [1, 2, 3]
myArray = myArray * 2
myArray = [1, 2, 3, 1, 2, 3]
Indexing elements
Want to have certain elements always together
Careful with arithmetic manipulation, because might not act as you’d expect
Whatever is on the RIGHT of the equals will be put together and the thing on the LEFT of the equals will have this value
Computer knows the order of the things in you list, so you can use the index (list position) of each item to call it forward

14. Functions Allows you to easily recall a procedure or subroutine
def sum(a, b):
return a+b
Parameters
values in the call, that you pass to the function to use as input
Output
Return value
Call Function
answer = sum(7,3)
answer = 10
Exact syntax will depend on the coding language
Define a function (write the part of the code)
Call a function (use this pre-written code)
- need to “pass” it a set of parameters
- like a mathematical function, need some input
Computer will “return” a value
Can then set a variable ot be the output of a certain function, if passed inputs

15. Functions Example function that returns a value def greet(name):
print "Hello " + name
Advantages
Repeat code, call multiple times
Flexible, call with different arguments
Functions
greet("Sue")
Can pass the function a list of inputs to avoid typing the same thing repeteticly.

16. Booleans True or False Useful for comparisons
Greater than, less than
Is equal to, is not equal to
Supports algebraic operations
and, or, not
A variable can have the VALUE of True or False
Be careful using these words in code if not using as values
Computer will understand value as true or false
can then ask computer whether something is true or false
“Looking at my set of data: is the concentration greater than 10 mM and color is yellow?”

17. If Statements and Loops
If this statement is true, do something
For loops
For all values in an array, do something repeatedly
While loops
While a statement is true, do something repeatedly
Way of asking a question to your computer – will evaluate data and make a decision for you
Different types of loops for different reasons – use the best one to maximize the efficiency of your code

18. Understanding the code

19. Computers do what you tell them
They are fast but not smart
You need to plan exactly what the computer needs to do in order to solve a problem
Outline the solution to your problem
Pseudocoding (step by step walkthrough of code)
The computer reads the code as written – syntax is important
YOU NEED TO PSEUDOCOE to outline and understand the logic behind the problem solving
Good way of double checking

20. Algorithms Describe in words how to solve a problem
Like a recipe, must be detailed and precise
How to make a Peanut Butter & Jelly Sandwich
Ingredients:
Two slices of bread
Peanut Butter
Jelly
Spread peanut butter on one slice
Spread jelly on the other slice
Combine slices together
Does this provide enough information for anyone to make the sandwich?
Always ask yourself FIRST how to explain how to solve the problem in words
Variables: ingredients
Algorithm: instructions
Broke code will often be missing a key logical part

21. How To Dissect Code Important information about function and usage
Opening a romeo.txt file
Counting something
Looping through lines
Example of ok code
Need more descriptive title
Need comments throughout
Need better, more useful header (what program used, etc)
Like how you can change the language of your Word document spell check
This done in a text editor, which is why the code has colors, line numbers, and etc to help you read the code
First variable: filename with the string value of “romeo.txt”
fileToProcess with a value of the output of the function “open” on the variable “filename”
Indentation at line 10 indicates that we are within some loop – can see that it is a for-loop
If you don’t know part of a code, you can always Google part of the code, or certain terms, with the language of code you are using
Aka google: strip() python
== means “if equal to”
So this will add 1 to the count, then restart the loop until the list of words is exhausted
Splitting lines into words?
Words of length 4?
Increase counter
Print count at the end

22. Computers Read In Order
Because this code is out of logical order (the computer reads sequentially), the computer does not know what to do at line 9 because it does not recognized the non-declared variable fileToProcess

23. Important Resources Sakai webpage howtolearntocode.web.unc.edu
HtLtC teachers
Stackoverflow.com
ITS Research Computing

24. Questions?