Simple rock, paper, scissors game

Question

I wrote a "Rock, paper, scissors" game:

puts "Hello, this is a rock, papers, scissors game. Let's play."
puts "Player 1, plase enter your choice: \n"
puts "r for rock. \np for paper. \ns for scissors."
p1 = gets.chomp.downcase

puts "Player 2, please enter your choice: \n"
puts "r for rock. \np for paper. \ns for scissors."
p2 = gets.chomp.downcase

if p1 == 'r' && p2 == 's'
  puts "Player 1 wins."
elsif p1 == 'r' && p2 == 'p'
  puts "Player 2 wins."
elsif p1 == 'r' && p2 == 'r'
  puts "Tie."
elsif p1 == 'p' && p2 == 'r'
  puts "Player 1 wins."
elsif p1 == 'p' && p2 == 's'
  puts "Player 2 wins."
elsif p1 == 'p' && p2 == 'p'
  puts "Tie."
elsif p1 == 's' && p2 == 'r'
  puts "Player 2 wins."
elsif p1 == 's' && p2 == 'p'
  puts "Player 1 wins."
elsif p1 == 's' && p2 == 's'
  puts "Tie."
end

It works, however, that's a lot of elsifs, and I know that this is possible with case...when statements, the thing is that I can't figure out how.

I was trying to use a return statement depending on the input: "return 0 for rock, 1 for paper and 2 for scissors", and then use a conditional to say something like "hey, if player one returns 1 and player 2 also returns 1, then puts 'tie'", and the same for the other possible results.

I was trying to associate a number to the result: return - 1 when player one wins, return 0 for a tie, and return 2 for player two wins.

I did it like this, but it's kind of the same, and I feel that it's so bad:

case p1
when p1 == 'r' && p2 == 'r'
  result = 0
when p1 == 'r' && p2 == 'p'
  result = 1
when p1 == 'r' && p2 == 's'
  result = -1
when p1 == 'p' && p2 == 'r'
  result = -1
when p1 == 'p' && p2 == 'p'
  result = 0
when p1 == 'p' && p2 == 's'
  result = 1
when p1 == 's' && p2 == 'r'
  result = 1
when p1 == 's' && p2 == 'p'
  result = -1
when p1 == 's' && p2 == 's'
  result = 0
end

if result == -1
  puts "P1 wins"
elsif result == 0
  puts "Tie"
elsif result == 1
  puts "P2 wins"
end

I would appreciate any kind of help.

This is a question for codereview.stackexchange.com – Mark Thomas Mar 01 '15 at 00:16 — Mark Thomas, Mar 01 '15 at 00:16

score 1 · Accepted Answer · answered Mar 01 '15 at 02:22

An array can be used as a ring, with each item having a weaker item to its right, and a stronger one to its left.

weapons = ['paper', 'rock', 'scissors']

select weapons by your favorite means

w1 = weapons[rand(weapons.length)]
w2 = weapons[rand(weapons.length)]

rotate array till w1 is at the center

while weapons[1] != w1
    weapons.rotate! 1
end

now the result is indicated by the index of w2 in weapons array, conveniently.

verbs = ['is beat by', 'ties', 'beats']
puts "#{w1} #{verbs[weapons.index(w2)]} #{w2}"

Example output from a few runs:

paper beats rock
paper ties paper
rock beats scissors
scissors beats paper
rock is beat by paper

You could get creative and add a hash of verb-arrays, one for each weapon, using w1 as the key so that it would output (for example) paper covers rock, etc.

Thank you so much for that, very clear. But sorry, what does it mean the 1 in `weapons.rotate! 1` ?. Also very helpful, since I was looking for a way of do it randomly, I mean, when playing against the computer, which should pick a random choice. — Leonardo Guedez, Mar 01 '15 at 04:33
The 1 is the number of elements to rotate. Really it wasn't necessary to specify because 1 is the default, but I did anyway. [Here's some documentation](http://ruby-doc.org//core-2.2.0/Array.html#method-i-rotate). — codess, Mar 01 '15 at 05:46

potashin · Answer 2 · 2015-03-01T00:18:28.077

0

You can try something like this :

if (p1 == p2)
  puts "Tie"
elsif (p1 == 'r' && p2 == 'p') ||
      (p1 == 'p' && p2 == 's') ||
      (p1 == 's' && p2 == 'r')
  puts "P2 wins"
else
  puts "P1 wins"
end

edited Mar 01 '15 at 00:18

answered Mar 01 '15 at 00:15

potashin

44,205
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107

Hey thanks! I tried it and works perfectly, and so much simpler than mine. – Leonardo Guedez Mar 01 '15 at 00:30

score 0 · Answer 3 · answered Mar 01 '15 at 00:34

0

You could also do the ruby equivalent of saying

  If p1 = 'r' then

goto R endif If p1 = 'p' then goto S endif

etc.

then at your goto locations later

R:

if p2 = 'r' then puts "tie"

etc.

however the idea of p1 = p2 then ... is a good one.

answered Mar 01 '15 at 00:34

Domnu Tous

1

`goto` is rumoured to be an experimental feature in v2.4. – Cary Swoveland Mar 01 '15 at 02:09
@Dommu Tous Hey thanks, I like it to see different approaches for the same result. However, although I don't consider myself an experienced programmer, I have seen a lot of bad things about the `goto` and recommendations of to not use it unless it's extremely necessary. Also, shouldn't be `if p1 == 'r' then`, with ==? – Leonardo Guedez Mar 01 '15 at 04:15

score 0 · Answer 4 · answered Mar 01 '15 at 03:06

Here's another way:

WINNERS = {s: :p, p: :r, r: :s}
  # => {:s=>:p, :p=>:r, :r=>:s} 

def win_lose_or_tie?(me, you)
  return "I win! :-)"   if WINNERS[me] == you 
  return "you win! :-(" if WINNERS[you] == me
  "it's a tie :-|"
end

keys = WINNERS.keys
keys.product(keys).each { |me, you|
  puts "If I play #{me} and you play #{you}, then #{win_lose_or_tie?(me, you)}" }
  # If I play s and you play s, then it's a tie :-|
  # If I play s and you play p, then I win! :-)
  # If I play s and you play r, then you win! :-(
  # If I play p and you play s, then you win! :-(
  # If I play p and you play p, then it's a tie :-|
  # If I play p and you play r, then I win! :-)
  # If I play r and you play s, then I win! :-)
  # If I play r and you play p, then you win! :-(
  # If I play r and you play r, then it's a tie :-|

score -1 · Answer 5 · answered Mar 01 '15 at 01:05

I'd use a case/when statement like:

result = case [p1, p2]
         when %w[r r], %w[p p], %w[s s]
           0
         when %w[r p], %w[p s], %w[s r]
           1
         when %w[r s], %w[p r], %w[s p]
           -1
         end

puts case result
     when  0
      "Tie"
     when -1
      "P1 wins"
     when  1
      "P2 wins"
     end

But, after writing that this makes more sense:

puts case [p1, p2]
        when %w[r r], %w[p p], %w[s s]
          'Tie'
        when %w[r p], %w[p s], %w[s r]
          'P1 wins'
        when %w[r s], %w[p r], %w[s p]
          'P2 wins'
        end

Here's a test:

[
  %w[r r], %w[p p], %w[s s],
  %w[r p], %w[p s], %w[s r],
  %w[r s], %w[p r], %w[s p]
  ].each do |p1, p2|

    puts case [p1, p2]
         when %w[r r], %w[p p], %w[s s]
           'Tie'
         when %w[r p], %w[p s], %w[s r]
           'P1 wins'
         when %w[r s], %w[p r], %w[s p]
           'P2 wins'
         end

  end
# >> Tie
# >> Tie
# >> Tie
# >> P1 wins
# >> P1 wins
# >> P1 wins
# >> P2 wins
# >> P2 wins
# >> P2 wins

Wow that looks great, I find the second option pretty neat, and thanks for the `%w` bit, I have never seen it before, pretty handy. — Leonardo Guedez, Mar 01 '15 at 04:24

Simple rock, paper, scissors game

5 Answers5