Variables and
Expressions, continued
CMSC 201
Expressions
Anything on the right hand side of an assignment is an
expression. An expression is anything that yields a
value.
a = 4
b = 10 * a
c = (100 * 4) // 9 + 2
# This is a function call,
# which we’ll discuss later.
d = sin(40)
Operators
Some basic operators:
Operation
Python Operator
Addition
+
Subtraction
-
Multiplication
*
Division
/
Exponentiation
**
Modulus
%
//
Operators
Exponentiation:
number ** power
So if we want 3 squared, we say:
3 ** 2
If we want 2 cubed, it would be:
2 ** 3
Modulus
Modulus:
a % b
gives “the remainder of a after a is divided by b”
14 % 6 == 2
12 % 2 == 0
10 % 3 == 1
Modulus
Why 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. Floats
Data 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!
Integer vs. Float Division
a = 7
b = 3
print(a/b)
prints 2.33333333
a = 7
b = 3
print(a//b)
prints 2
Integers vs. Floats
When we divide a float and anything else, the result is a
float. However, there is often rounding error.
7.0 / 3.0
2.3333333333333335
Be careful to never compare two floats after you have
done division!
What happens if you print this???
print(2.3333333333333333)
Other Math Functions
Other math functions:
from math import *
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