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Part 3: Keeping Our Balance
4:20In part 3 of Build a Bank Account class, we're going to calculate the balance based off of all of the transactions that exist within the account. We do this by writing a method called `balance`.
Okay, so we've got our BankAccount class
all set up.
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And we've get credits, debits, and
transactions going on.
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So it would be nice to be able to see what
our balance is.
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So let's go ahead and write a method that
calculates the balance for
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us by looping through the transactions.
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So we know that transactions is an array.
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And in the Ruby Loops course,
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we learned about iterating through arrays
with the each method.
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Let's go ahead and use the each method to
iterate over the transactions and
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add up the balance.
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So, we can say @transactions.each do.
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|transaction|
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This will iterate over the @transactions
array and
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pass each item into this little code
block.
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And now we'll create a local variable,
which we're just gonna call balance.
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And then we'll add on to the balance in
each transaction.
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So, we'll say the balance is equal to
whatever it was before,
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plus the amount of this transaction.
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[SOUND] And then, we can return the
balance.
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[BLANK_AUDIO]
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Now we know that the transaction amount is
gonna be positive or negative.
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We know that because we're going to be
calling the credit and
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debit methods each time we add on to the
transactions.
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So we know that when there's a debit, this
goes in as a negative amount.
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And credits go in as a positive amount.
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Therefore, adding on to the balance will
work as we expect it to,
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because adding a negative number is the
same as subtraction.
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So now instead of this inspect method,
let's go ahead and print out the balance.
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And that functions exactly as we
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expect it to by returning 60.
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Now what would happen if we made this 0.0?
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Well, it prints out 60.0.
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Now if we wanted this to print out like
currency,
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say having 60.0 and instead we want 60.00,
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we can use a method called sprintf to
format this particular string.
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You can read the documentation for this if
you'd like to find out a little bit more.
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The string that we need to use, is a
percent,
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a zero, a dot, a two, and an f.
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Which means it's going to print this
floating point number to two decimals.
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So if we run this again, it prints out
60.00 just like we expect.
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Now that we have this balance method all
set up, let's go ahead and
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override the to string method to print
that all out.
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So to_s, we'll say the name is the name
that we initialized the class with.
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And the balance is the balance.
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And you know what, let's go ahead and call
balance just like we do here.
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[BLANK_AUDIO]
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Now this is a little tricky,
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because we're doing string interpolation
inside of another string.
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So we can go down here.
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And just print out the bank account.
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So now, it says name Jason and the balance
is 60.00.
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In our next video, we'll be printing out a
formatted register.
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