commit d3b743e98c584d782ae08396cbdc71c4f8853262
Author: wc <975706314@qq.com>
Date:   Thu Oct 8 01:16:23 2015 +0800

    20151008 homework

diff --git a/ruby_intro.rb b/ruby_intro.rb
new file mode 100644
index 0000000..51a5274
--- /dev/null
+++ b/ruby_intro.rb
@@ -0,0 +1,134 @@
+# When done, submit this entire file.
+
+# Part 1
+
+def sum arr
+  # YOUR CODE HERE
+  	arr_sum = 0
+  	arr.each do |i|
+  		arr_sum += i
+  	end
+  	return arr_sum	
+end
+
+def max_2_sum arr
+  # YOUR CODE HERE
+  	arr_max2sum = 0
+  	sort_arr = arr.sort
+  	if  sort_arr[-1] != nil
+  		arr_max2sum += sort_arr[-1]
+  		if  sort_arr[-2] != nil
+  			arr_max2sum += sort_arr[-2]
+  		end
+  	end
+  	return arr_max2sum
+end
+
+def sum_to_n? arr, n
+  # YOUR CODE HERE
+  	arr_length = arr.length
+  	if arr_length==0
+  		if n==0
+  			return true
+  		else
+  			return false
+  		end
+  	end
+  	if arr_length==1
+  		if n==arr[0]
+			return true
+		else
+			return false
+		end  		
+  	end
+  	first=0
+  	begin
+  		second=first+1
+  		begin
+  			if arr[first] + arr[second] == n
+  				return true
+  			end
+  			second += 1
+  		end until second > arr_length-1
+  		first += 1
+  	 end until first > arr_length-2
+  	 return false
+end
+
+# Part 2
+
+def hello(name)
+  # YOUR CODE HERE
+  	a = "Hello, "
+  	return a << name
+end
+
+def starts_with_consonant? s
+  # YOUR CODE HERE
+  	no_consonant = "aeiou"
+  	if s[0] != nil
+  		start_down = s[0].downcase
+  	        start_up = s[0].upcase
+  		if start_down != start_up
+  			if  !(no_consonant.include? start_down)
+  				return true
+  			end
+  		end
+  	end
+  	return false
+end
+
+def binary_multiple_of_4? s
+  # YOUR CODE HERE
+        if s[0]==nil
+                return false
+        end
+        s.each_char do|character|
+                if character.to_i.to_s != character   or  character.to_i > 1
+                        return false
+                end
+        end
+        if (s.to_i(2) % 4) == 0
+                return true
+        else
+                return false
+        end
+end
+
+# Part 3
+
+class BookInStock
+# YOUR CODE HERE
+        def initialize (isbn, price)
+                if isbn.empty? or price < 0
+                        raise ArgumentError, 'the argument is not propert'
+                end
+                @isbn = isbn
+                @price = price
+        end
+        def price_as_string
+                price_string = @price.to_s
+                price_string.insert(0, '$')
+                dot_index = price_string.index('.')
+                if dot_index == nil
+                        price_string << ".00"
+                        return price_string
+                end
+                if price_string[-2] == '.'
+                        price_string << "0"
+                        return price_string
+                end
+                price_string = price_string[0..(dot_index + 2)]
+                return price_string
+        end
+end
+
+#arr = [1,2,3]
+#puts "The sum is #{sum arr}"
+#puts "The max 2 sum is #{max_2_sum arr}"
+#puts "The sum_to_n? is #{sum_to_n? arr, 1}"
+#puts "The hello(name) is #{hello("wangcan")}"
+#puts "The starts_with_consonant is #{starts_with_consonant? "01110"}"
+#puts "The binary_multiple_of_4 is #{binary_multiple_of_4? "01100"}"
+#book1 = BookInStock.new("0915", 20)
+#puts "#{book1.price_as_string}"
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