A Really Quick Introduction to Programming

With examples using python.

• Statement: A command given to the computer.
• Assign a value of -9.8 to a variable called “g”:

g = -9.8

• Print the value of “g” to the screen:

print g 

• Variable: A placeholder name used to record data for later use. In the first statement above, g, is a variable and it is assigned a value of -9.8. Variable names in python start with a letter or underscore “_”. Variables can hold different types of data, for example:
• strings:

x = "hello"

• Floating point number (aka. a float):

x = 9.8

• Integer:

x = 5

• True/False (aka boolean):

x = True 

• Operations: Statements where some sort of calculation is made:
• Add two numbers and assign the result to a variable called “y”:

y = 3 + 5

• Divide the value in the variable “y” by 2 and then assign the value to another variable called “z”:

z = y / 2

• Operators: The symbols that tell what operation to do:
• + – * / are used for addition, subtraction, multiplication, and division respectively
• ** is used for exponents so 5 squared (5²) is:

a = 5**2

• Loops: Tell the computer to do something over and over again. There are different types:
• “For” loops are good for doing things a set number of times

for i in range(5):
	print i

results in:

0
1
2
3
4

• Logical statements: These test to see if something is True or False and then do different things based on the outcome:
• Assign a value to a variable called “x”, check to see if the value is greater than 10, and print out a different sentence based on the result:

x = 12
if (x > 10):
	print "x is greater than 10"
else:
	print "x is less than 10"

• Functions: Chunks of code that someone (maybe even you) wrote that can be referenced via a shortcut:
Create a function to calculate the force of gravity at the Earth’s surface if you give it a mass:

def forceOfGravity(mass):
	Fg = mass * -9.8
	return Fg

Call the function to find the force of gravity acting on a mass of 100 kg and print out the result:

x = forceOfGravity(100)
print x

the result should be:

-980

• Classes: A class is like a function that you can assign to a variable and then have it do a lot more stuff.
In vpython there is a class called “sphere”. It renders a 3d sphere on the screen. Here we’ll create a sphere, assign it to a variable “ball” and then change one of its built-in properties, the color, from the default (white) to red. (if you are using Glowscript.org then don’t use the first line that imports the visual module).

from visual import *
ball = sphere()
ball.color = color.red