Style, Conventions, and Debugging

Indentation

Just as it's used in a traditional essay's outline, indentation is used by programmers to indicate nested elements and subroutines. In Ruby, the interpreter pays no mind to it. It's purely for human readability.

One of the most common programming constructs is the loop, which executes a given block of code a given number of times. Try this out:

3.times.each do |num|
   puts "start of the block..."
   puts num
   puts "...ending the block"
end

The output should look like this:

start of the block...
0
...ending the block
start of the block...
1
...ending the block
start of the block...
2
...ending the block

The first and last line defines the loop. The lines in between consist of the subroutine, or block that is to be repeated. A loop within a loop would have another level of indentation:

3.times.each do |x|
   puts "In the first loop"
   4.times.each do |y|
      puts "In the second loop "
      puts x * y
   end
end

And to reiterate the point about whitespace being insignificant in Ruby, the following code is equivalent to the code above, albeit harder to read:

3.times.each do |x|
puts "In the first loop"
4.times.each do |y|
puts "In the second loop "
puts x * y
end
end

I use the tab key to indent. Other programmers prefer to double-space. Most programming text-editors are smart enough to indent subsequent lines – just as Microsoft Word will automatically indent and number items in a numbered list after you type in something like: "1. A first step..."

Whitespace exceptions

There are various exceptions to how freely you can use whitespace. Again, it's hard to get into specifics without being more familiar with the language.

Carriage returns between operations: In general, don't hit Enter to break up an operation. For example, this:

puts "hello"

– is not equivalent to this:

puts
"hello"

However, this:

2 + 2 + 2

– can actually be written as this:

2 + 2
+ 2 

– but why would you do it? It's going to confuse anyone else who reads it.

The following involves a conditional statement, something we cover a few chapters down the road:

if 4 == 2 + 2
   puts "Ergo, 2+2 is not 5"
end

– and it is not equivalent to this:

if 4 
   == 2 + 2
   puts "Ergo, 2+2 is not 5"
end

The elements of the conditional statement (4 == 2 + 2, i.e. "Is four equal to two plus two?") need to be on the same line – again, don't worry about knowing why yet. Just stick to what makes intuitive sense: why would you do the extra work of separating a statement with a line break like that?

The =begin and =end comment block:

When setting an entire block of code to be commented out with =begin and =end, those two keywords must be on their own lines, with no whitespace preceding them. So this:

=begin
these 
   are comments
=end   

– and not this:

 =begin
this will NOT be a comment
=end

=begin
 this is OK
   =end
  And the above =end did NOT close this section of comments   

Deduce the unfamiliar

Copy and paste the following code into your text editor (or irb) and execute it:

c, d = "X++-"[0..1].split('').map{|x| x[0].to_i*1*4*"9"[0] }
c * rand + 100; puts c; c*d - (c==9+'a'[3].to_i ? 3.14 : (
c==d ? 12 * 6.62606957*rand(100*c*d) :? rand(c+(9*c)) )); a = [42,12]; puts a.compact.map{|x| 
d -= 9 +'a'[3].to_i+('?'.to_i+100) *5.12 
x.to_s.upcase.to_i *rand(12) }.join("||!@ --")
c * (rand(10) *rand(5020 + c) * ran(d*1000) + rand(c))
c+d-c* 64.001*rand(3.141516 * 100.0101 * c)
e = a.each_with_index.map{|r, i| a[i] = a[i] * -2 }

You should get an error like this:

/Users/dnguyen/ttest.rb:3: warning: invalid character syntax; use ?\s
/Users/dnguyen/ttest.rb:3: syntax error, unexpected '?'
... * 6.62606957*rand(100*c*d) :? rand(c+(9*c)) )); a = [42,12]...

At this stage, most of the words above probably make no sense. Where are you supposed to use ?\s. What's a rand? And forget about understanding the actual code: I don't even know what it does and I just made it up.

So just focus on what you do know. Below, I've highlighted what appears to be the filename:

/Users/dnguyen/ttest.rb:3: warning: invalid character syntax; use ?\s
/Users/dnguyen/ttest.rb:3: syntax error, unexpected '?'
... * 6.62606957*rand(100*c*d) :? rand(c+(9*c)) )); a = [42,12]...

What's the :3 stand for? Considering the code is only 8 lines long, and that there happens to be a couple of question marks on line 3, you can reasonably guess that :3 stands for Line 3.

So there's an unexpected '?' on Line 3, but there are two of them in the code:

c==d ? 12 * 6.62606957*rand(100*c*d) :? rand(c+(9*c)) )); a = [42,12]; puts a.compact.map{|x| 

Let's go back to the error message and focus on the line that actually says error:

/Users/dnguyen/ttest.rb:3: syntax error, unexpected '?'
... * 6.62606957*rand(100*c*d) :? rand(c+(9*c)) )); a = [42,12]...

The error message has helpfully pointed out the excerpt of Line 3 with the question mark. Let's take it out and see what happens; copy and execute the code below:

c, d = "X++-"[0..1].split('').map{|x| x[0].to_i*1*4*"9"[0] }
c * rand + 100; puts c; c*d - (c==9+'a'[3].to_i ? 3.14 : (
c==d ? 12 * 6.62606957*rand(100*c*d) : rand(c+(9*c)) )); a = [42,12]; puts a.compact.map{|x| 
d -= 9 +'a'[3].to_i+('?'.to_i+100) *5.12 
x.to_s.upcase.to_i *rand(12) }.join("||!@ --")
c * (rand(10) *rand(5020 + c) * ran(d*1000) + rand(c))
c+d-c* 64.001*rand(3.141516 * 100.0101 * c)
e = a.each_with_index.map{|r, i| a[i] = a[i] * -2 }   

And you'll get another error. I've highlighted the parts that most resemble English:

20064
0||!@ --11
NoMethodError: undefined method ‘ran’ for main:Object 
   at top level   in ttest.rb at line 6

We know from past experience that the reported line number – Line 6, in this case – is pretty accurate. And though we don't know why an undefined method is bad, there is apparently one such thing with the name of 'ran'. So let's look at Line 6:

c * (rand(10) *rand(5020 + c) * ran(d*1000) + rand(c))

So ran isn't right, but what is it supposed to be? Well, there's some use of the term rand; it's possible that the programmer made a typo. So tack on the letter 'd' and see what happens:

c, d = "X++-"[0..1].split('').map{|x| x[0].to_i*1*4*"9"[0] }
c * rand + 100; puts c; c*d - (c==9+'a'[3].to_i ? 3.14 : (
c==d ? 12 * 6.62606957*rand(100*c*d) : rand(c+(9*c)) )); a = [42,12]; puts a.compact.map{|x| 
d -= 9 +'a'[3].to_i+('?'.to_i+100) *5.12 
x.to_s.upcase.to_i *rand(12) }.join("||!@ --")
c * (rand(10) *rand(5020 + c) * rand(d*1000) + rand(c))
c+d-c* 64.001*rand(3.141516 * 100.0101 * c)
e = a.each_with_index.map{|r, i| a[i] = a[i] * -2 }   

You get this non-sensical output:

20064
42||!@ --6

But there's no error message. So at least that's off our backs! There's nothing more we can really do since we were given no insight on what the program is supposed to do. But fixing the show-stopping errors on an indecipherable chunk of code without knowing what it does – or, if you're new to this, not knowing code period – was just a matter seeing past the clutter and following directions.

Using puts is not just for putz

There are specialized debugger programs that give a more sophisticated picture of the internal workings of your code. But oftentimes, especially for small scripts, it's quicker to directly "ask" a buggy program what it is doing at each step of the way.

In the installation guide, we ran our first program:

puts "Hello world"

All it did was print out to the screen:

Hello world

So, even without knowing that puts is a method – or that "Hello world" is a string – we can assume for now that puts puts things on the screen for us to read.

The following program is supposed to simply print out a message comparing values in the variables a and b:

a = 1 + 1
b = 2 + 2

if a = b
   puts "a is equal to b"
elsif a > b
   puts "a is greater than b"
elsif a < b 
   puts "a is less than b"
end   

Without knowing exactly what variables are, or what the if/elsif statements are about, you can still deduce the gist of it: I mentioned previously that this program will print out a message comparing a and b. Since a and b seem to be set equal to the values of 2 and 4, respectively (1 + 1 and 2 + 2), you probably are surprised to see this as the output of the program:

a is equal to b

Step-by-step

Well, it's possible that + doesn't mean what it did in elementary school. So lets modify the code to insert a couple of puts statements to see what's actually in a and b:

a = 1 + 1
b = 2 + 2
 
puts "a is: "
puts a

puts "b is:"
puts b

if a = b
   puts "a is equal to b"
elsif a > b
   puts "a is greater than b"
elsif a < b 
   puts "a is less than b"
end   

And the output is:

a is: 
2
b is:
4
a is equal to b

So addition works. And yet the value of a is clearly not equal to the value in b. So let's move those puts statements to test if the equals sign in if a = b does the comparison that we assume it to do:

a = 1 + 1
b = 2 + 2

if a = b
 
   puts "a is: "
   puts a

   puts "b is:"
   puts b
    
   puts "a is equal to b"

elsif a > b
   puts "a is greater than b"
elsif a < b 
   puts "a is less than b"
end

And the output of that code is:

a is: 
4
b is:
4
a is equal to b

Bingo. It appears that the equals sign in if a = b is setting the value of a equal to the value in b

Well, maybe that's what the program is supposed to do – who knows? And (at least until we get to the conditionals chapter to find out what really is supposed to be in that if statement) we don't know how to fix it, but at least we can report it to the proper authority.