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Well done!
You have completed Ruby Basics!
You have completed Ruby Basics!
Preview
If you try to treat a string like a number, you may get strange results. Let's learn how to convert strings that contain a number to actual numbers.
- If you use the
*operator on a string, it repeats the string the number of times you supply. - That can give you strange results if you try to treat a string containing a number as if it was an actual number.
puts "A" * 10 # AAAAAAAAAA
puts "7" * 10 # 7777777777
- We need to use one of these methods to convert the string to an actual number before multiplying it.
puts "7".to_i * 10 # 70
Widget store
Let's use the to_i method to convert the string the user entered to an actual number, then multiply the result:
def ask(question)
print question + " "
gets.chomp
end
puts "Welcome to the widget store!"
answer = ask("How many widgets are you ordering?")
number = answer.to_i
puts "For #{number} widgets, your total is: $#{number * 10}"
Output:
Welcome to the widget store!
How many widgets are you ordering? 7
For 7 widgets, your total is: $70
Additional practice
We've created a workshop where you can get additional practice working with numbers in Ruby. Don't miss this chance to strengthen your skills!
Visit the workshop here: Practice Ruby Numeric Types
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Now that we understand math operations,
let's see if we can
0:00
use to multiply the quantity of widgets
by 10 to get a total price for the order.
0:03
We'll update the call to puts to
print the number of widgets entered and
0:08
then the same number multiplied by 10.
0:11
So say, for whatever number
the user entered, answer, widgets.
0:14
Your total is, We'll put a dollar sign,
0:23
and then we'll interpolate in whatever
the user's answer was, times 10.
0:30
Let's save this, and
try running it, ruby widgets.rb.
0:36
How many widgets are you ordering?
0:43
Let's put in seven.
0:45
For 7 widgets, your total is
0:47
$7777777777.
0:52
Maybe my math is wrong, but
that doesn't seem right to me.
0:56
Now interestingly,
1:01
we still have a call to the p method,
printing the value in answer.
1:02
And down here at the bottom, it's printing
out 7 as if it was a string, not a number.
1:06
Let's confirm that by calling the class
method on value in our answer variable.
1:12
We'll run that again.
1:17
And sure enough,
it's a String, not a number.
1:22
Let's get rid of that debug code,
we're not gonna need that anymore.
1:25
If you use the multiplication
operator with a String and a Fixnum,
1:29
it's going to repeat the String that many times,
so if we take the String with
1:32
the letter "a" and multiply that three times,
we get a string consisting of "aaa".
1:37
We don't want that happening
with the value the user enters.
1:43
So we're going to need to convert
the String to an actual number before
1:45
multiplying it.
1:48
Let's look at the documentation for
the string class.
1:51
Let's see if there any methods
that we'll help us with this.
1:53
So, we'll type ruby to
limit the results to
1:56
sites that are on the ruby language and
then string.
2:00
To bring up info on the string class.
2:04
We'll go at the top result, here.
2:06
And if we scroll down the side here,
we're eventually see a method named to_f.
2:09
Let's take a look at that.
2:13
And it looks like String.to_f will convert the
String to a floating point number,
2:15
which is good, but not perfect.
2:20
Because we're ordering a number of
widgets, and it seems unlikely that we're
2:22
ever going to want one and a half widgets,
we're only going to want a whole number.
2:26
So instead, perhaps we would be
more interested in this to_i method
2:30
which converts the String to an integer.
2:34
So let's try that in our code instead.
2:37
We'll create a new variable and number.
2:40
And we'll assign that the result
of calling the to_i method on
2:43
the String that's in the answer variable.
2:47
So it will take the String
that's in answer.
2:50
And convert it to an integer.
2:52
And assign the result to number.
2:54
Then, instead of the answer variable
down here in our puts method column,
2:56
we'll use number.
3:01
And we'll say your total is number
times 10, not answer times 10.
3:05
That should multiply the integer,
not the String.
3:10
Let's save this and try running it.
3:13
Ruby widgets.rb.
3:18
How many widgets are you ordering?
3:20
We're gonna say 7, and this time
we get the correct answer, $70 or
3:22
seven times 10.
3:27
Converting the String to an integer
before multiplying it worked.
3:28
In this stage we've covered the basics
of working with numbers in Ruby.
3:32
Check the teacher's notes for ways you
can get more practice with numbers and
3:36
math operations.
3:39
Now that you know the basics
of math operations in Ruby,
3:42
calculating a total price is easy.
3:44
Nice work, you've implemented three of
the four features our program needs,
3:47
just one more to go.
3:51
Our last requirement is to offer
discounts for large orders.
3:53
If a user orders 50 widgets or more,
we wanna charge them $9 per widget.
3:56
And for orders of 100 or more,
we wanna charge only $8 each.
4:01
If they're ordering 50,
we charge 9 a piece.
4:06
If they're ordering 100,
we charge 8 a piece.
4:09
We don't really know of a way to
change our program's behavior under
4:12
different conditions yet.
4:15
In the final stage of this course,
we'll show you how.
4:18
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