Numbers
Numbers
The following operations work on numbers:
- + -- addition
- - -- subtraction
- * -- multiplication
- / -- division
- % -- modulus
- ** -- exponentiation
LAB: Playing With Numbers
Answer the following questions using irb:
- How many seconds are in an hour?
- How many minutes are in a week?
- How many seconds old are you?
- How many years old is someone who is 1 billion seconds old?
Order of operations
Q: What is 1 plus 2 times 3?
Order of operations
Q: What is 1 plus 2 times 3?
A: It depends!
-
(1 + 2) * 3is 9 -
1 + (2 * 3)is 7
Parentheses Are Free
When in doubt, use parentheses!
Strings vs. Numbers
Hmmm....
1 + 2 "1" + "2" "1 + 2"
Strings plus Numbers
Hmmm again...
"1" + 2
Uh-oh!
TypeError: can't convert Fixnum into String
The problem is that Strings and Numbers are different TYPES, aka different CLASSES.
Don't panic! The solution is easy.
Type Conversion
Numbers know a message that converts them into strings. to_s means "to string".
"1" + 2.to_s
Likewise, strings know a message that converts them into numbers.
1 + "2".to_i
to_i means "to integer".
Try this in irb!
Advanced Number Theory (optional)
WTFixnum?
The error said can't convert Fixnum into String.
Q: What is a Fixnum?
A: It's one type of number.
Math is hard
There are many types of numbers!
Each is useful in different situations.
Without getting into too much detail, the two main number types in Ruby are:
-
Fixnum- for integers like 12 or -1023 -
Float- for decimals like 3.14
(Other number types include Complex, Rational, and Bignum.)
Number to Number
You can convert from one type of number to another by sending a message:
-
to_iturns a Float into a Fixnum -
to_fturns a Fixnum into a Float
Try this:
3.to_f 3.14.to_i
String to Number
to_f and to_i also work on Strings:
"3.14".to_f "3.14".to_i
and to_s works on numbers:
3.14.to_s
Arithmetic
Try this in irb:
1 + 2 3 - 4 5 * 6 7 / 8
Whoa! What just happened?
Integer Arithmetic
7 and 8 are Integers
so the result is an Integer
7/8 is somewhere between 0 and 1
but there is no integer between 0 and 1
so the computer has to round down to 0
Floating Point Arithmetic
7.0/8.0
7.0 and 8.0 are Floats
so the result is a Float
and 0.875 can fit in a float