ArtBears · May 10, 2013 07:17 · May 10, 2013
diff --git a/CardTrick.rb b/CardTrick.rb
@@ -0,0 +1,97 @@
+=begin
+ This is a number analogy to a famous card trick.
+ Ask the user to enter a three-digit number. Think
+ of the number as ABC (where A, B, C are the three 
+ digits of the number). Now, find the remainders of 
+ the numbers formed by ABC, BCA, and CAB when divided 
+ by 11. We will call these remainders X, Y, Z. Add 
+ them up as X+Y, Y+Z, Z+X. If any of the sums are odd,
+ increase or decrease it by 11 (whichever operation 
+ results in a positive number less than 20; note if 
+ the sum is 9, just report this and stop the process). 
+ Finally, divide each of the sums in half. The 
+ resulting digits are A, B, C. Write a program that 
+ implements this algorithm.
+=end
+
+def first_number(x)
+  p = x.to_i % 100
+  q = ((x.to_i - p.to_i) / 100)
+  return q
+end
+
+def second_number(x)
+  p = ((x.to_i % 100) * 10) / 100
+  return p
+end
+
+def third_number(x)
+  p = x.to_i % 10
+  return p
+end
+
+def find_remainder(hundreds, tens, ones)
+  hundreds = hundreds.to_i * 100
+  tens = tens.to_i * 10
+  new_number = (hundreds + tens + ones) % 11
+  return new_number
+end
+
+def is_odd(x)
+  if (x % 2) == 0 
+    return false
+  else return true
+  end
+end
+
+def less_than_20(x)
+  if x < 9  
+    x = (x + 11) / 2
+  elsif x > 9
+    x = (x-11) / 2
+  else
+    return x
+  end
+  return x
+end
+
+def equation(x, y, z)
+  u = x + y
+  p = y + z
+  s = z + x
+  if is_odd(u) == true 
+    u = less_than_20(u)
+  else
+    u = u / 2
+  end
+
+  if(is_odd(p) == true)
+    p = less_than_20(p)
+  else
+    p = p / 2
+  end
+
+  if(is_odd(s) == true)
+    s = less_than_20(s)
+  else
+    s = s / 2
+  end
+
+  puts  "A: " << u.to_s
+  puts  "B: " << p.to_s
+  puts  "C: " << s.to_s
+end
+
+puts "Enter a 3 digit number: "
+abc = gets.chomp
+if (abc.to_i > 99 && abc.to_i < 1000) 
+  a = first_number(abc)
+  b = second_number(abc)
+  c = third_number(abc)
+  x = find_remainder(a,b,c)
+  y = find_remainder(b,c,a)
+  z = find_remainder(c,a,b)
+  equation(x,y,z)
+else
+  puts "The integer must be 3 digits!"
+end
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