Discussion on compiler and symbol table, including Hashing technique.

1. Introduction of Symbol Table

2. What kind of work is done in Compiler LAB
Sessional?
 Lexical analysis
 Syntax analysis
 Syntax-directed translation
 Semantic analysis
 type-checking
 Run-time environments
 Intermediate code generation
 Code generation
 Code optimization.

3. THE STRUCTURE OF A COMPILER
Converts source program semantically into equivalent target
program.

4. Function of a compiler
 Record the variable names used in the source program.
 Collect information about various attributes.
Provide information on storage allocation for
 Name
 Type
 Scope
 Procedure names
 Argument types
 Argument passing method
 Type return type

5. Compiler structure

6. What is symbol table?
Data structures used by compilers for holding
information about source-program.
a int LB1 UB1 SYMBOL TABLE pointer steers the symbol table to
remotely stored information for array

7. Symbol tables typically need to support multiple
declarations of the same identifier within a program

8. Use of Symbol Table
 Generating intermediate or target code.
 For verifying used identifiers have been
defined.
 For verifying expressions & assignments are
semantically correct – type checking.
 Information is used by the analysis and
synthesis phases.

9. Hashing
A symbol table can be implemented
in one of the following ways:
 Linear (sorted or unsorted) list
 Binary Search Tree
 Hash table

10. Why use Hashing in Symbol Table?
Common data structure.
 Must be organized for quicker search.
keyword or identifier is 'hashed' to produce an array
subscript.

11. #include<iostream>
#include<stdlib.h>
using namespace std;
class Symbol_Info
{
public:
string Symbol_Type;
string Symbol_Name;
};
struct node
{
Symbol_Info ob;
struct node *Next;
};
typedef struct node Node;
class Link_list
{
int s ;
Node *Head[];
public:
Link_list(int n)
{
s=n;
for(int i=0; i<n; i++)
{
Head[i]=NULL;
}
}
void insert_Node()
{
int index;
Node *temp=new Node;
temp->Next=NULL;
cout<<"Token Name: ";
cin>>temp->ob.Symbol_Name;
cout<<"Token Type: ";
cin>>temp->ob.Symbol_Type;
index=Type_Match(temp-
>ob.Symbol_Type);
if(index==-1)
{
cout<<"nInvalid tokenn";
return;
}
if( Head[index] == NULL)
{
Head[index]=temp;

12. else
{
temp->Next=Head[index];
Head[index]=temp;
}
}
void Print_List()
{
for(int i=0; i<s; i++)
{
Node *temp=Head[i];
while(temp)
{
cout<<"<"<<temp-
>ob.Symbol_Name<<","<<temp->ob.Symbol_Type<<">-
--";
temp=temp->Next;
}
cout<<"n";
}
}
void Delete_List()
{
int index;
string N,T;
int flag=0;
cout<<"Token Name: ";
cin>>N;
cout<<"Token Type: ";
cin>>T;
index=Type_Match(T);
Node **H=&(Head[index]);
if(index==-1)
{
cout<<"Invalid Token";
return;
}
if(Head[index]==NULL)
{
cout<<"nList is Emptyn";
return;
}
if((*H)->ob.Symbol_Name==N && (*H)-
>ob.Symbol_Type==T)
{
*H=(*H)->Next;
}
else
{
Node *temp1=*H;
Node *temp2=(*H)->Next;
while(temp2)
{
if(temp2-
>ob.Symbol_Name==N&&temp2-
>ob.Symbol_Type==T)

13. {
flag=1;
break;
}
temp1=temp1->Next;
temp2=temp2->Next;
}
if(flag==1)
{
temp2=temp2->Next;
temp1->Next=temp2;
return;
}
cout<<"nToken not in listn";
}
}
int Type_Match(string type)
{
if(type=="INT"||type=="STRING"||type=="FLOAT"||type=="CHAR"||type=="STRUCT"||type=
="LONG")
return 0;
if(type=="NUM")
return 1;
if(type=="OP"||type=="RELOP"||type=="ARITh"||type=="SMCLN"||type=="COMMA")
return 2;
if(type=="COND"||type=="LOOP")
return 3;
if(type=="FUNC")

14. return 4;
return -1;
}
};
int main()
{
int n;
cout<<"Measurement : ";
cin>>n;
Link_list List(n);
int ch;
while(1)
{
cout<<endl;
cout<<"1 : Input"<<endl<<"2 : Display"<<endl<<"3 : Erase"<<endl<<"4 :
Stop"<<endl;
cout<<"Enter Your Choice : ";
cin>>ch;
if(ch==1)
{
cout<<endl;
List.insert_Node();
cout<<endl;
}
if(ch==2)

15. {
cout<<endl;
List.Print_List();
cout<<endl;
}
if(ch==3)
{
cout<<endl;
List.Delete_List();
cout<<endl;
}
if(ch==4)
{
exit(0);
}
}
return 0;
}