Variables and Expressions, continued

CMSC 201

ExpressionsAnything on the right hand side of the equals is an expression. Expressions can be anything that yields a value.

a = 4b = 10 * ac = (100 * 4) / 9 + 2d = sin(40) # This is a function call, which we’ll

# discuss later.

OperatorsSo what can we do in python? Here are some basic operators:

Operation Python Operator

Addition +

Subtraction -

Multiplication *

Division /

Exponentiation **

Modulus %

OperatorsExponentiation:

number ** power

So if we want 3 squared, we say:

3 ** 2

If we want 2 cubed, it would be:

2 ** 3

ModulusModulus:

a % b

Is equivalent to “the remainder of a after a is divided by b”

14 % 6 = 212 % 2 = 010 % 3 = 1

ModulusWhy is modulus useful?

• Tells us if one thing is divisible by another (if you mod a by b and get zero, b is divisible by a)

• Remainders are useful! Imagine you know the first of a month is a Monday, and you want to know what day the 27th is. All you need to do is figure out 27 % 7, and that’s how many days past Monday you are.

Integers vs. FloatsData in python remembers what type it is.

a = 4

a is an integer.

b = 4.4

b is a float.

Floats and integers act differently!

Integers vs. FloatsWhen we divide a float and anything else, the result is a float. However, there is often rounding error.

>> 7.0 / 3.02.3333333333333335

Be careful to never compare two floats after you have done division!

Other Math FunctionsUsing “import math” we can access other math functions, such as:

Function Purpose

cos(x), sin(x), tan(x) Trigonometric functions

log(x, base) Logarithm of x with given base

floor(x) Finds the closest integer less than or equal x

ceil(x) Finds the closest integer greater than or equal to x

sqrt(x) Finds the square root of x

pi The value of pi

E The value of e