diff --git a/version0.7/lr_pda_demo.cpp b/version0.7/lr_pda_demo.cpp
new file mode 100644
index 0000000..4ee3972
--- /dev/null
+++ b/version0.7/lr_pda_demo.cpp
@@ -0,0 +1,179 @@
+#include <list>
+#include <stack>
+#include <cstring>
+#include <iostream>
+
+enum token_type
+{
+	S=1,a,T,__tri,__comma,__left_curve,__right_curve,sharp
+};
+
+const int max_len=5;
+struct cmp_seq
+{
+	int tokens[max_len];
+	int res;
+};
+cmp_seq par[]=
+{
+	{{a},                            S},
+	{{__tri},                        S},
+	{{__right_curve,T,__left_curve}, S},
+	{{S},                            T},
+	{{T,__comma,T},                  T},
+};
+int num_of_par=sizeof(par)/sizeof(cmp_seq);
+
+void print_token(int type)
+{
+	std::string context="";
+	switch(type)
+	{
+		case sharp:
+			context="#";
+			break;
+		case S:
+			context="S";
+			break;
+		case a:
+			context="a";
+			break;
+		case T:
+			context="T";
+			break;
+		case __tri:
+			context="^";
+			break;
+		case __comma:
+			context=",";
+			break;
+		case __left_curve:
+			context="(";
+			break;
+		case __right_curve:
+			context=")";
+			break;
+	}
+	std::cout<<context;
+	return;
+}
+
+class PDA
+{
+	private:
+		std::stack<int> main_stack;
+		std::stack<int> comp_stack;
+	public:
+		PDA(std::string& text)
+		{
+			main_stack.push(sharp);
+			for(int i=0;i<(int)text.length();++i)
+			{
+				if(text[i]=='(')
+					main_stack.push(__left_curve);
+				else if(text[i]==')')
+					main_stack.push(__right_curve);
+				else if(text[i]=='a')
+					main_stack.push(a);
+				else if(text[i]=='^')
+					main_stack.push(__tri);
+				else if(text[i]==',')
+					main_stack.push(__comma);
+			}
+			comp_stack.push(sharp);
+		}
+		void print_stack(std::stack<int>& temp)
+		{
+			std::stack<int> t;
+			while(!temp.empty())
+			{
+				t.push(temp.top());
+				print_token(t.top());
+				temp.pop();
+			}
+			while(!t.empty())
+			{
+				temp.push(t.top());
+				t.pop();
+			}
+			return;
+		}
+		void print_main_and_comp()
+		{
+			print_stack(main_stack);
+			std::cout<<"		";
+			print_stack(comp_stack);
+			std::cout<<std::endl;
+			return;
+		}
+		bool reducable()
+		{
+			std::stack<int> temp;
+			for(int i=0;i<num_of_par;++i)
+			{
+				for(int j=max_len-1;j>=0;--j)
+				{
+					if(!par[i].tokens[j])
+						continue;
+					// if par[i].tokens[j] is 0 then continue until the tokens[j] is not 0
+					temp.push(comp_stack.top());
+					comp_stack.pop();
+					if((par[i].tokens[j]!=temp.top()) || (comp_stack.empty() && par[i].tokens[j]))
+					{
+						while(!temp.empty())
+						{
+							comp_stack.push(temp.top());
+							temp.pop();
+						}
+						break;
+					}
+					if((par[i].tokens[j]==temp.top()) && (j==0))
+					{
+						comp_stack.push(par[i].res);
+						return true;
+					}
+				}
+			}
+			return false;
+		}
+		void work()
+		{
+			print_main_and_comp();
+			while(main_stack.top()!=sharp)
+			{
+				
+				comp_stack.push(main_stack.top());
+				main_stack.pop();
+				while(1)
+				{
+					if(!reducable())
+						break;
+					print_main_and_comp();
+				}
+			}
+			print_main_and_comp();
+			if(comp_stack.top()==T)
+			{
+				comp_stack.pop();
+				if(comp_stack.top()==sharp)
+					std::cout<<"accept."<<std::endl;
+				else
+					std::cout<<"error."<<std::endl;
+			}
+			else
+				std::cout<<"error."<<std::endl;
+			return;
+		}
+};
+
+int main()
+{
+	std::string text;
+	while(1)
+	{
+		std::cin>>text;
+		PDA m(text);
+		m.work();
+	}
+	return 0;
+}