diff --git a/parser.c b/parser.c
new file mode 100644
index 0000000000000000000000000000000000000000..cad097348463b78d3defc0215b46a10264a83b88
--- /dev/null
+++ b/parser.c
@@ -0,0 +1,380 @@
+#include<stdio.h>
+#include<string.h>
+#include<stdlib.h>
+#include"parser.h"
+
+Tree* A();
+Tree* A_(Tree * a_);
+Tree* E();
+Tree* E_(Tree * e_);
+Tree* T();
+Tree* T_(Tree * t_);
+Tree* F();
+Tree* F_();
+
+Tree* mkTree(TOKEN type,char*vl);
+
+int not_defined(TOKEN_LIST t[]);
+void match(int a);
+void syntax_error();
+void do_syntax_analysis();
+double cal(Tree* rtnode);
+void Free_tree(Tree* node);
+
+int s_error;
+int l;
+int index_location;
+
+void do_syntax_analysis()
+{
+ s_error = 0;
+ index_location = 0;
+ l = token_list[index_location].token;
+ Tree* root = A();
+ if(s_error == 1||index_location+1!=token_number)
+ {
+ printf("syntax error\n");
+ Free_tree(root);
+ return;
+ }
+ if(not_defined(token_list) == 1)
+ {
+ Free_tree(root);
+ return;
+ }
+ double result = cal(root);
+ if(result-(int)(result)==0)
+ {
+ printf("%d\n",(int)(result));
+ }
+ else
+ {
+ printf("%f\n",result);
+ }
+ Free_tree(root);
+ return;
+}
+
+Tree* A()
+{
+ if(l==1)
+ {
+// printf("A->idA'\n");
+ Tree* temp1 = mkTree(token_list[index_location].token,token_list[index_location].value);
+ match(1);
+ return A_(temp1);
+ }
+ else if(l==9|l==2|l==3|l==5)
+ {
+// printf("A->F'T'E'\n");
+ Tree* temp2;
+ temp2 = F_();
+ temp2 = T_(temp2);
+ return E_(temp2);
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* A_(Tree* a_)
+{
+ if(l==4|l==5|l==6|l==7|l==0)
+ {
+// printf("A'->T'E'\n");
+ a_ = T_(a_);
+ a_ = E_(a_);
+ return a_;
+ }
+ else if(l==8)
+ {
+// printf("A'->=A\n");
+ Tree* temp3 = mkTree(token_list[index_location].token,token_list[index_location].value);
+ match(8);
+ temp3->left = a_;
+ temp3->right = A();
+ return temp3;
+ }
+
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* E()
+{
+ if(l==1|l==9|l==2|l==3|l==5)
+ {
+// printf("E->TE'\n");
+ Tree* temp15;
+ temp15 = T();
+ temp15 = E_(temp15);
+ return temp15;
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* E_(Tree* e_)
+{
+ if(l==10|l==0)
+ {
+// printf("E'->e\n");
+ match(0);
+ return e_;
+ }
+ else if(l==4)
+ {
+// printf("E'->+TE'\n");
+ Tree* temp4 = mkTree(token_list[index_location].token,"+");
+ match(4);
+ temp4->left = e_;
+ temp4->right = T();
+ return E_(temp4);
+ }
+ else if(l==5)
+ {
+// printf("E'->-TE'\n");
+ Tree *temp5 = mkTree(token_list[index_location].token,"-");
+ match(5);
+ temp5->left = e_;
+ temp5->right = T();
+ return E_(temp5);
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* T()
+{
+ if(l==1|l==9|l==2|l==3|l==5)
+ {
+// printf("T->FT'\n");
+ Tree* temp14;
+ temp14 = F();
+ temp14 = T_(temp14);
+ return temp14;
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* T_(Tree *t_)
+{
+ if(l==10|l==5|l==4|l==0)
+ {
+// printf("T'->e\n");
+ match(0);
+ return t_;
+ }
+ else if(l==6)
+ {
+// printf("T'->*FT'\n");
+ Tree *temp6 = mkTree(token_list[index_location].token,"*");
+ match(6);
+ temp6 -> left = t_;
+ temp6 -> right = F();
+ return T_(temp6);
+ }
+ else if(l==7)
+ {
+// printf("T'->/FT'\n");
+ Tree * temp7 = mkTree(token_list[index_location].token,"/");
+ match(7);
+ temp7 -> left = t_;
+ temp7 -> right = F();
+ return T_(temp7);
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* F()
+{
+ if(l==1)
+ {
+// printf("F->id\n");
+ Tree * temp8 = mkTree(token_list[index_location].token,token_list[index_location].value);
+ match(1);
+ return temp8;
+ }
+ else if(l==9|l==2|l==3|l==5)
+ {
+// printf("F->F'\n");
+ return F_();
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree* F_()
+{
+ if(l==9)
+ {
+// printf("F'->(E)\n");
+ Tree* temp12;
+ match(9);
+ temp12 = E();
+ match(10);
+ return temp12;
+ }
+ else if(l==2)
+ {
+// printf("F'->int\n");
+ Tree* temp11 = mkTree(token_list[index_location].token,token_list[index_location].value);
+ match(2);
+ return temp11;
+ }
+ else if(l==3)
+ {
+// printf("F'->Double\n");
+ Tree* temp13 = mkTree(token_list[index_location].token, token_list[index_location].value);
+ match(3);
+ return temp13;
+ }
+ else if(l==5)
+ {
+// printf("F'->-F\n");
+ Tree* temp9 = mkTree(token_list[index_location].token,"-");
+ match(5);
+ temp9->left = F();
+ return temp9;
+ }
+ else
+ {
+ syntax_error();
+ return NULL;
+ }
+}
+
+Tree * mkTree(TOKEN type,char*vl)
+{
+ Tree * temp1 = (Tree*)malloc(sizeof(Tree));
+ temp1->left = NULL;
+ temp1->right = NULL;
+ temp1->token_type = type;
+ strcpy(temp1->token_value,vl);
+ return temp1;
+}
+void Free_tree(Tree * node)
+{
+ if(node!=NULL)
+ {
+ Free_tree(node->left);
+ Free_tree(node->right);
+ free(node);
+ }
+}
+
+void match(int look_ahd)
+{
+ if(look_ahd!=0)
+ {
+ if(look_ahd==token_list[index_location].token)
+ {
+ index_location = index_location+1;
+ l = token_list[index_location].token;
+ }
+ else
+ {
+ syntax_error();
+ return;
+ }
+ }
+}
+int not_defined(TOKEN_LIST t[])
+{
+ for(int i=0;i<token_number;i++)
+ {
+ if(t[i].token==1)
+ {
+ if(t[i+1].token!=8&&symbol_table[find_symbol(t[i].value)].set_up==0)
+ {
+ printf("%s is not defined\n",t[i].value);
+ return 1;
+ }
+ }
+ }
+ return 0;
+}
+
+void syntax_error()
+{
+ s_error = 1;
+}
+
+double cal(Tree* rtnode)
+{
+ double temp_1,temp_2;
+ while(rtnode!=NULL)
+ {
+ if(rtnode->token_type == 1)
+ {
+ return symbol_table[find_symbol(rtnode->token_value)].value.real_constant;
+ }
+ if(rtnode->token_type == 2)
+ {
+ return atof(rtnode->token_value);
+ }
+ if(rtnode->token_type == 3)
+ {
+ return atof(rtnode->token_value);
+ }
+ if(rtnode->token_type == 4)
+ {
+ temp_1 = cal(rtnode->left);
+ temp_2 = cal(rtnode->right);
+ return temp_1+temp_2;
+ }
+ if(rtnode->token_type == 5)
+ {
+ if(rtnode->left == NULL && rtnode->right == NULL)
+ break;
+ if(rtnode->right == NULL)
+ return -cal(rtnode->left);
+ else
+ {
+ temp_1 = cal(rtnode->left);
+ temp_2 = cal(rtnode->right);
+ return temp_1 - temp_2;
+ }
+ }
+ if(rtnode->token_type == 6)
+ {
+ temp_1 = cal(rtnode->left);
+ temp_2 = cal(rtnode->right);
+ return temp_1*temp_2;
+ }
+ if(rtnode->token_type == 7)
+ {
+ temp_1 = cal(rtnode->left);
+ temp_2 = cal(rtnode->right);
+ return temp_1 / temp_2;
+ }
+ if(rtnode->token_type == 8)
+ {
+ symbol_table[find_symbol(rtnode->left->token_value)].value.real_constant = cal(rtnode->right);
+ symbol_table[find_symbol(rtnode->left->token_value)].set_up=1;
+ return symbol_table[find_symbol(rtnode->left->token_value)].value.real_constant;
+ }
+ }
+}