The following operations work on numbers:
Answer the following questions using irb:
Q: What is 1 plus 2 times 3?
Q: What is 1 plus 2 times 3?
A: It depends!
(1 + 2) * 3
is 91 + (2 * 3)
is 7When in doubt, use parentheses!
Hmmm....
1 + 2 "1" + "2" "1 + 2"
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.
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!
The error said can't convert Fixnum into String
.
Q: What is a Fixnum?
A: It's one type of number.
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 -1023Float
- for decimals like 3.14(Other number types include Complex, Rational, and Bignum.)
You can convert from one type of number to another by sending a message:
to_i
turns a Float into a Fixnumto_f
turns a Fixnum into a FloatTry this:
3.to_f 3.14.to_i
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
Try this in irb:
1 + 2 3 - 4 5 * 6 7 / 8
Whoa! What just happened?
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
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
/
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