Ruby exercise using ARGV

Question

I have to create the following pattern:

*
**
***
****
*****

Using a ARGV and this is what I have so far:

height = ARGV[0]
output = ""


height.to_i.times do |i|
  output << "*" * i
  output << "\n"
end
puts output

But every time I run ruby pyramid.rb 5 on my mac terminal, I get the following output:

$ ruby pyramid.rb 5

*
**
***
****

Why is it giving me 4 when it needs to have 5 of them?

I've edited the output - note the empty line? That's `"*" * 0`, as describe in [Chris Schmich's answer](http://stackoverflow.com/a/32751643/477037) — Stefan, Sep 24 '15 at 06:53

score 4 · Answer 1 · edited May 23 '17 at 12:06

4

Integer#times yields values from 0 to n-1, so you're getting lines of 0 up to 4 stars.

You mentioned this was an exercise, so I'll leave the fix up to you.

In general, to troubleshoot these kinds of problems, it's best to use a debugger or add diagnostic printing (e.g. puts statements) to trace the values of variables and ensure they're what you expected.

For example, in this case, you could add puts i inside your loop to see what the value of i is at every iteration. You would see something like 0 1 2 3 4 printed, which isn't what you expected. From there, you can look at your code, documentation, or add more diagnostic output to determine why you get those values.

edited May 23 '17 at 12:06

Community

1
1

answered Sep 24 '15 at 00:44

Chris Schmich

29,128
5
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Thanks for the reply and explanation. Yes, its an exercise done from the beginning. Our only instruction was that we needed to use `height = ARGV` and `output = ""` as our variables. Still scratching my head on how to get that final piece that I am missing. – jBntz Sep 24 '15 at 01:51
1

There are a couple approaches: 1) What would you need to do to `i` in your loop to have it be `1` to `5` instead of `0` to `4` as it is now? or 2) Consider looking at the [upto](http://ruby-doc.org/core-2.2.0/Integer.html#method-i-upto) method and how you could use that here – Chris Schmich Sep 24 '15 at 04:00

score 0 · Answer 2 · answered Mar 02 '19 at 11:20

I know this thread is old but I felt it's better late than never. Chris hinted at the solution. If i is starting from zero, you just have to make it so that i starts from 1 by simple adding i += 1. see example below:

height = ARGV[0]
output = ""
height.to_i.times do |i|
  i += 1
  output << "*" * i
  output << "\n"
end
puts output

Todd A. Jacobs · Answer 3 · 2019-03-17T09:41:11.997

Analysis

The problem in your code is the use of Integer#times. Per the documentation, the #times method:

[i]terates the given block int times, passing in values from zero to int - 1.

So, here is your given code, with comments:

height.to_i.times do |i| # when `height = 5`, equivalent to `(0..4).each`
  output << "*" * i      # will be "" on the first pass when i == 0
  output << "\n"
end

Solution

In this case, you should use the Integer#upto method instead of Integer#times, with 1 as your starting value. Consider the following example, rewritten as a one-liner you can run from the command prompt:

$ ruby -e '1.upto(Integer(ARGV[0])) { |i| puts "*" * i }' 5
*
**
***
****
*****

In addition to giving the expected results on standard output, it also does away with string mutation, declaring an output variable, and other non-essentials. The use of Kernel#Integer will also raise an exception if ARGV[0] can't be cast as an integer, rather introducing subtle bugs such as when ARGV[0] == "".

Ruby exercise using ARGV

3 Answers3

Analysis

Solution