What is a programming language?

Humans use languages (English, Urdu, Arabic) to communicate with each other. A program is a set of instructions that tells a computer what to do. Programs are written using a programming language. A programming language, then, is used by humans to communicate with computers.

There is still a language barrier between computers and humans. Computers understand machine language. Machine language is often times platform specific. Code generated on one machine may not run on another machine. Machine language looks like this:

| Instruction Binary Code  | 
| 0010 0001 0000 0100  | 
| 0001 0001 0000 0101  | 
| 0011 0001 0000 0110  |
| 0111 0000 0000 0001  | 
| 0000 0000 0101 0011  | 
| 0000 0000 0101 0011  |
| 0000 0000 0000 0000  |

This notation is very difficult for humans to understand. This is where assembly languages come in. Assembly language consists of a set of symbols and letters which a translator uses to translate to machine language. This translator is called the ‘assembler.’

ORG 100 
LDA A
ADD B
STA C
HLT
A, DEC 83
B, DEC –2
C, DEC 0
END

We can sort of see what this program is doing. However, this form of communication is still not intuitive for humans. Some progress must be made.

A high level programming language uses English logic (if, while, for, then, else) and mathematical symbols (+, -, %, |, &) to communicate with a computer. These programs are compiled into machine code by a compiler. Compilation does not imply execution of the code. It just referes to the conversion from a high level programming language to machine code. The advantage here is that these high level programming languages are portable. I can code on my laptop and run it on my desktop.

int a, b, c;
a = 83;
b = -2;
c = a + b;

Credit: http://people.uncw.edu/tompkinsj/242/BasicComputer/AddTwoNumbers.htm

Variables

Variables are used to store information. A variable can hold many different types of information:

String: "abc", "hello", "YAM"
Integer: 2, -5, 6, 100000
Float: 2.0, 5.66, -9.89
Boolean: true, false
Char: 'y', 'A', 'm'

How to create variables?

Variables are easy with Python:

first_name = "Khurram"
last_name = "Ghullamani"
age = 22
height = 65
married = false
spouse = ""

What can you do with them?

//update the varibale completely
first_name = "Chandler"
last_name = "Bing"
married = true
spouse = "Monica"

// perform mathematical operations
age = age + 30
height -= 2

// random stuff
my_number = age + height

// string concatenation -- Chandler Bing
full_name = first_name + " " + last_name

What can’t you do with them?

// type checking
age + name --->> ERROR
married+age ---->> ERROR
first_name-last_name ---->> ERROR

Functions

A function is a piece of code that can be used to execute multiple code statements over and over again. Example:

def my_first_function(age):
	age = age + 10
	return age

Here, def is keyword reserved in Python. It is used to declare a function. The name of the function is “my_first_function”. It takes a parameter known as age. A parameter is simply information that the user can pass into the function. The two lines after are known as the function body. This function takes the age, adds 10 and returns (gives the user back) the new value. After your return, your program is over. Example:

my_age = 22
new_age = my_first_function(my_age)

// new_age now equals 22 + 10 = 32

Variable Scope in functions

A variable can be global or local. Example:

def my_height_function(user_height):
	my_height = 65
	new_height = my_height + user_height
	return new_height

my_height = my_height + 10 ------>> ERROR

In the example above, my_height is a local variable. It was defined in the scope of the function. It cannot be used outside the function. We could switch our definition to look like this:

my_height = 65
def my_height_function(user_height):
	new_height = my_height + user_height
	return new_height

my_height = my_height + 10 ------>> This is correct

Since my_height is defined outside the function, it can be used inside the function as well as outside the function. This is an example of a global variable.

Activity

Let’s run your first program. What do you think this does?

import webbrowser
url = "https://www.google.com/#q="
def search_for():
	query = raw_input("What would you like to search for?")
	my_url = url + query
	webbrowser.open(my_url)

search_for()

Clone this repositiory

Complete the problems in the file assignment.py. Then run the tests in the file test_assignment.py using the command: python test_assignmet.py. See how many you can get correct