One More Example
I think another example method would be helpful here. We’ll call this one english_number. It will take a number, like 22, and return the English version of it (in this case, the string 'twenty-two'). For now, let’s have it work only on integers from 0 to 100:
def english_number number |
|
# We accept numbers from 0 to 100. |
|
if number < 0 |
return 'Please enter a number zero or greater.' |
end |
if number > 100 |
return 'Please enter a number 100 or less.' |
end |
|
num_string = '' # This is the string we will return. |
|
# "left" is how much of the number |
# we still have left to write out. |
# "write" is the part we are |
# writing out right now. |
# write and left... get it? :) |
left = number |
write = left/100 # How many hundreds left? |
left = left - write*100 # Subtract off those hundreds. |
|
if write > 0 |
return 'one hundred' |
end |
|
write = left/10 # How many tens left? |
left = left - write*10 # Subtract off those tens. |
|
if write > 0 |
if write == 1 # Uh-oh... |
# Since we can't write "tenty-two" |
# instead of "twelve", we have to |
# make a special exception for these. |
if left == 0 |
num_string = num_string + 'ten' |
elsif left == 1 |
num_string = num_string + 'eleven' |
elsif left == 2 |
num_string = num_string + 'twelve' |
elsif left == 3 |
num_string = num_string + 'thirteen' |
elsif left == 4 |
num_string = num_string + 'fourteen' |
elsif left == 5 |
num_string = num_string + 'fifteen' |
elsif left == 6 |
num_string = num_string + 'sixteen' |
elsif left == 7 |
num_string = num_string + 'seventeen' |
elsif left == 8 |
num_string = num_string + 'eighteen' |
elsif left == 9 |
num_string = num_string + 'nineteen' |
end |
|
# Since we took care of the digit in the |
# ones place already, we have nothing left to write. |
|
left = 0 |
elsif write == 2 |
num_string = num_string + 'twenty' |
elsif write == 3 |
num_string = num_string + 'thirty' |
elsif write == 4 |
num_string = num_string + 'forty' |
elsif write == 5 |
num_string = num_string + 'fifty' |
elsif write == 6 |
num_string = num_string + 'sixty' |
elsif write == 7 |
num_string = num_string + 'seventy' |
elsif write == 8 |
num_string = num_string + 'eighty' |
elsif write == 9 |
num_string = num_string + 'ninety' |
end |
|
if left > 0 |
num_string = num_string + '-' |
end |
end |
|
write = left # How many ones left to write out? |
left = 0 # Subtract off those ones. |
if write > 0 |
if write == 1 |
num_string = num_string + 'one' |
elsif write == 2 |
num_string = num_string + 'two' |
elsif write == 3 |
num_string = num_string + 'three' |
elsif write == 4 |
num_string = num_string + 'four' |
elsif write == 5 |
num_string = num_string + 'five' |
elsif write == 6 |
num_string = num_string + 'six' |
elsif write == 7 |
num_string = num_string + 'seven' |
elsif write == 8 |
num_string = num_string + 'eight' |
elsif write == 9 |
num_string = num_string + 'nine' |
end |
end |
if num_string == '' |
# The only way "num_string" could be empty |
# is if "number" is 0. |
return 'zero' |
end |
# If we got this far, then we had a number |
# somewhere in between 0 and 100, so we need |
# to return "num_string". |
num_string |
end |
|
puts english_number( 0) |
puts english_number( 9) |
puts english_number( 10) |
puts english_number( 11) |
puts english_number( 17) |
puts english_number( 32) |
puts english_number( 88) |
puts english_number( 99) |
puts english_number(100) |
zero |
nine |
ten |
eleven |
seventeen |
thirty-two |
eighty-eight |
ninety-nine |
one hundred |
Well, I certainly don’t like this program very much. First, it has too much repetition. Second, it doesn’t handle numbers greater than 100. Third, it has too many special cases and too many returns. Let’s use some arrays and try to clean it up a bit. Plus, we can use recursion for handling large numbers, since when we write out 123,123,123 (giving us “one hundred twenty-three million, one hundred twenty-three thousand, one hundred twenty-three”), we write “one hundred twenty-three” exactly the same three times. So, here we go:
def english_number number |
if number < 0 # No negative numbers. |
return 'Please enter a number that isn't negative.' |
end |
if number == 0 |
return 'zero' |
end |
|
# No more special cases! No more returns! |
num_string = '' # This is the string we will return. |
|
ones_place = ['one', 'two', 'three', |
'four', 'five', 'six', |
'seven', 'eight', 'nine'] |
tens_place = ['ten', 'twenty', 'thirty', |
'forty', 'fifty', 'sixty', |
'seventy', 'eighty', 'ninety'] |
teenagers = ['eleven', 'twelve', 'thirteen', |
'fourteen', 'fifteen', 'sixteen', |
'seventeen', 'eighteen', 'nineteen'] |
# "left" is how much of the number |
# we still have left to write out. |
# "write" is the part we are |
# writing out right now. |
# write and left...get it? :) |
left = number |
write = left/100 # How many hundreds left? |
left = left - write*100 # Subtract off those hundreds. |
|
if write > 0 |
# Now here's the recursion: |
hundreds = english_number write |
num_string = num_string + hundreds + ' hundred' |
if left > 0 |
# So we don't write 'two hundredfifty-one'... |
num_string = num_string + ' ' |
end |
end |
|
write = left/10 # How many tens left? |
left = left - write*10 # Subtract off those tens. |
|
if write > 0 |
if ((write == 1) and (left > 0)) |
# Since we can't write "tenty-two" instead of |
# "twelve", we have to make a special exception |
# for these. |
num_string = num_string + teenagers[left-1] |
# The "-1" is because teenagers[3] is |
# 'fourteen', not 'thirteen'. |
# Since we took care of the digit in the |
# ones place already, we have nothing left to write. |
left = 0 |
else |
num_string = num_string + tens_place[write-1] |
# The "-1" is because tens_place[3] is |
# 'forty', not 'thirty'. |
end |
|
if left > 0 |
# So we don't write 'sixtyfour'... |
num_string = num_string + '-' |
end |
end |
|
write = left # How many ones left to write out? |
left = 0 # Subtract off those ones. |
|
if write > 0 |
num_string = num_string + ones_place[write-1] |
# The "-1" is because ones_place[3] is |
# 'four', not 'three'. |
end |
|
# Now we just return "num_string"... |
num_string |
end |
|
puts english_number( 0) |
puts english_number( 9) |
puts english_number( 10) |
puts english_number( 11) |
puts english_number( 17) |
puts english_number( 32) |
puts english_number( 88) |
puts english_number( 99) |
puts english_number(100) |
puts english_number(101) |
puts english_number(234) |
puts english_number(3211) |
puts english_number(999999) |
puts english_number(1000000000000) |
zero |
nine |
ten |
eleven |
seventeen |
thirty-two |
eighty-eight |
ninety-nine |
one hundred |
one hundred one |
two hundred thirty-four |
thirty-two hundred eleven |
ninety-nine hundred ninety-nine hundred ninety-nine |
one hundred hundred hundred hundred hundred hundred |
Ahhhh…that’s much, much better. The program is fairly dense, which is why I put in so many comments. It even works for large numbers, though not quite as nicely as one would hope. For example, I think 'one trillion' would be a nicer return value for that last number, or even 'one million million' (though all three are correct). In fact, you can do that right now….
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