Sign In
Create Account
Follow Us on Twitter
Subscribe on Youtube
I am implementing SLR parser in my project. I got a code to construct parsing table and to parse a string. But it is not giving correct answer. Can u help me?
Thank u..
Code to find first and follow:
saved as SLR.h
#include<stdio.h>
#include<ctype.h>
#include<conio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream.h>
#define epsilon '^'
// since I didn't know how to type epsilon symbol temporily I am using ^
char prod[20][20],T[20],NT[20],c[10][10],foll[10][10],fir[10][10];
int tt,tnt,tp,a;
int follow[20][20],first[20][20];
void first_of(char);
int count(int j);
void rhs(int j);
void read_tnt();
int rhs(int j);
void read_tnt()
{
cout<<"For SLR parser: ";
cout<<"\nEnter number of terminals: ";
cin>>tt;
cout<<"\nEnter terminals: ";
for(int i=0;i<tt;i++)
T[i]=getche();
getch();
cout<<"\nEnter number of Non-terminals: ";
cin>>tnt;
cout<<"\nEnter Non-terminals: ";
for(i=0;i<tnt;i++)
NT[i]=getche();
getch();
}
void read_prod()
{
int j;
char x=0;
cout<<"\n\nEnter number of productions: ";
cin>>tp;
cout<<"\n Enter productions: ";
for(int i=0;i<tp;i++)
{
j=x=0;
while(x!='\r')
{
prod[i][j]=x=getche();
j++;
}
cout<<"\n";
}
getch();
}
int nt_no(char n)
{
for(int i=0;i<tnt;i++)
if(NT[i]==n)
return(i);
return(-1);
}
int t_no(char t)
{
for(int i=0;i<tt;i++)
if(T[i]==t)
return(i);
if(t=='$')
return(tt);
return(-1);
}
int terminal(char x)
{
for(int i=0;i<tt;i++)
if(T[i]==x)
return(1);
return(0);
}
int nonterminal(char x)
{
for(int i=0;i<tnt;i++)
if(NT[i]==x)
return(1);
return(0);
}
int in_rhs(char *s,char x)
{
for(int i=0;i<=strlen(s);i++)
if(*(s+i)==x)
return(i);
return(-1);
}
void find_first()
{
for(int i=0;i<tnt;i++)
first_of(NT[i]);
}
void first_of(char n)
{
int t1,t2,p1,cnt=0,i,j;
char x;
static int over[20];
p1=t_no(epsilon);
if(terminal(n))
return;
t1=nt_no(n);
if(over[t1])
return;
over[t1]=1;
for(i=0;i<tp;i++)
{
t1=nt_no(prod[i][0]);
if(prod[i][0]==n)
{
int k=0;
cnt=count(1);
rhs(i);
while(k<cnt)
{
x=c[i][k];
if(terminal(x))
{
t2=t_no(x);
first[t1][t2]=1;
break;
}
else
{
t2=nt_no(x);
first_of(x);
for(int j=0;j<tt;j++)
if(p1!=j && first[t2][j])
first[t1][j]=1;
if(p1!=-1 && first[t2][p1])
k++;
else
break;
}
}
if(p1!=-1 && k>=cnt)
first[t1][p1]=1;
}
}
}
void follow_of(char n)
{
int f,t1,t2,p1,t,cnt=0;
char x,beta;
static int over[20];
p1=t_no(epsilon);
t1=nt_no(n);
if(over[t1])
return;
over[t1]=1;
if(NT[0]==n)
follow[nt_no(NT[0])][tt]=1;
for(int i=0;i<tp;i++)
{
rhs(i);
cnt=count(i);
t=in_rhs(c[i],n);
if(t==-1)
continue;
for(int k=t+1;k<=cnt;k++)
{
rhs(i);
beta=c[i][k];
if(terminal(beta))
{
t2=t_no(beta);
follow[t1][t2]=1;
break;
}
int bno;
for(int j=0;j<tt;j++)
{
bno=nt_no(beta);
if((first[bno][j]) && (j!=p1))
follow[t1][j]=1;
}
if((p1!=-1) && (first[bno][p1]==1))
continue;
else if((t==(cnt-1)||(k>=cnt)))
{
follow_of(prod[i][0]);
t1=nt_no(prod[i][0]);
for(int l=0;l<=tt+1;l++)
if(follow[t][l])
follow[t1][l]=1;
}
}
}
}
int count(int j)
{
int c1=0;
for(int q=3;prod[j][q]!='\r';q++)
c1++;
return(c1);
}
void rhs(int j)
{
int a,h=0;
a=j;
for(int q=3;prod[j][q]!='\r';q++)
{
c[a][h]=prod[j][q];
h++;
}
}
void find_follow()
{
for(int i=0;i<tnt;i++)
follow_of(NT[i]);
}
void show_follow()
{
int b=0;
a=0;
cout<<"\n\n Follow Table For Grammar: \n";
for(int i=0;i<tnt;i++)
{
b=0;
cout<<"\n FOLLOW ("<<NT[i]<<" )= { ";
for(int j=0;j<tt+1;j++)
if(follow[i][j] && j!=tt)
{
foll[a][b]=T[j];
b++;
cout<<T[j]<<" ";
}
else
if(j==tt)
{
foll[a][b]='$';
b++;
cout<<'$';
}
a++;
cout<<" } ";
}
getch();
}
void show_first()
{
int b=0;
a=0;
cout<<"\n\n First Table For Grammar: \n";
for(int i=0;i<tnt;i++)
{
b=0;
cout<<"\n FIRST ("<<NT[i]<<" )= { ";
for(int j=0;j<tt+1;j++)
if(first[i][j] && j!=tt)
{
fir[a][b]=T[j];
b++;
cout<<T[j]<<" ";
}
a++;
cout<<" } ";
}
getch();
}
void mainf(void)
{
clrscr();
read_tnt();
read_prod();
find_first();
find_follow();
show_follow();
show_first();
}
To construct parse table:
#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<ctype.h>
#include<stdlib.h>
#include<iostream.h>
#include"c:\tc\bin\SLR.h"
int S=0,i=0,j=0,state[20];
char TNT[15];
struct node
{
int pno,dpos;
};
struct t
{
char s;
int n;
};
struct t1
{
struct t lr[10];
int gr[5];
};
struct t1 action[15];
struct node closure[10][10];
int g[15][10];
int l;
void sclosure(int,int);
int added(int);
int t_into(char);
void print_table(int);
void parser(void);
int find_index(char);
int t_ino(char);
void pop(void);
void push(char,int);
void find_closure(int,int);
void SLR(void);
void main()
{
clrscr();
mainf();
getch();
for(int i=0;i<tnt;i++)
TNT[i]=NT[i];
for(int j=0;j<tt;j++)
{
TNT[i]=T[j];
i++;
}
strcat(T,"$");
i=j=0;
SLR();
print_table(S);
getch();
// clrscr();
// parser();
// getch();
}
void SLR()
{
int clno,no=0,x,y,z,len,cnt=-1,d=0;
closure[i][j].pno=0;
closure[i][j++].dpos=3;
find_closure(no,3);
sclosure(i,j);
state[i]=j;
S=0;
do
{
cnt++;
z=state[cnt];
for(int k=0;k<tnt+tt;k++)
{
i++;
j=0;d=0;
for(int l=0;l<z;l++)
{
x=closure[cnt][1].pno;
y=closure[cnt][1].dpos;
if(prod[x][y]==TNT[k])
{
d=1;
closure[i][j].pno=x;
closure[i][j++].dpos=++y;
if((y<strlen(prod[x])) && (isupper(prod[x][y])))
find_closure(x,y);
}
}
if(d==0)
{
i--;
continue;
}
sclosure(i,j);
state[i]=j;
clno=added(i-1);
if(clno==-1)
clno=i;
if(isupper(TNT[k]))
action[cnt].gr[k]=clno;
else
{
action[cnt].lr[k-tnt].s='S';
action[cnt].lr[k-tnt].n=clno;
}
if(added(i-1)!=-1)
i--;
else
{
S++;
for(l=0;l<state[i];l++)
{
if(closure[i][1].pno==0)
{
action[i].lr[tt].s='A';
continue;
}
len=(strlen(prod[closure[i][l].pno])-1);
if(len==closure[i][l].dpos)
{
char v=prod[closure[i][l].pno][0];
int u=nt_no(v);
for(x=0;x<strlen(foll[u]);x++)
{
int w=t_ino(foll[u][x]);
action[i].lr[w].s='R';
action[i].lr[w].n=closure[i][l].pno;
}
}
}
}
}
}
while(cnt!=S);
}
void print_table(int states)
{
int lin=5;
cout<<"\n\n Parser Table: \n";
for(int i=0;i<tt;i++)
cout<<"\t"<<T[i];
cout<<"\t$";
for(i=0;i<tnt;i++)
cout<<"\t"<<NT[i];
cout<<"\n______________________________________________________________\n";
for(i=0;i<=states;i++)
{
gotoxy(l,lin);
cout<<"I"<<i<<"\t";
for(int j=0;j<=tt;j++)
{
if(action[i].lr[j].s!='\x0')
{
if(action[i].lr[j].s=='A')
{
cout<<"Acc";
continue;
}
cout<<action[i].lr[j].s;
cout<<action[i].lr[j].n;
cout<<"\t";
}
else
cout<<"\t";
}
for(j=0;j<tnt;j++)
if(action[i].gr[j])
{
cout<<action[i].gr[j];
cout<<"\t";
}
else
cout<<"\t";
lin++;
cout<<"\n";
}
cout<<"\n______________________________________________________";
}
void sclosure(int clno,int prodno)
{
struct node temp;
for(int i=0;i<prodno-1;i++)
{
for(int j=i+1;j<prodno;j++)
{
if(closure[clno][i].pno>closure[clno][j].pno)
{
temp=closure[clno][i];
closure[clno][i]=closure[clno][j];
closure[clno][j]=temp;
}
}
}
for(i=0;i<prodno-1;i++)
{
for(j=i+1;j<prodno;j++)
{
if((closure[clno][i].dpos>closure[clno][j].dpos) &&
(closure[clno][i].pno==closure[clno][j].pno))
{
temp=closure[clno][i];
closure[clno][i]=closure[clno][j];
closure[clno][j]=temp;
}
}
}
}
int added(int n)
{
int d=1;
for(int k=0;k<=n;k++)
{
if(state[k]==state[n+1])
{
d=0;
for(int j=0;j<state[k];j++)
{
if((closure[k][j].pno!=closure[n+1][j].pno) ||
(closure[k][j].dpos!=closure[n+1][j].dpos))
break;
else
d++;
}
if(d==state[k])
return(k);
}
}
return(-1);
}
void find_closure(int no,int dp)
{
int k;
char temp[5];
if(isupper(prod[no][dp]))
{
for(k=0;k<tp;k++)
{
if(prod[k][0]==prod[no][dp])
{
closure[i][j].pno=k;
closure[i][j++].dpos=3;
if(isupper(prod[k][3])&&
(prod[k][3]!=prod[k][0]))
find_closure(k,3);
}
}
}
return;
}
int t_ino(char t)
{
for(int i=0;i<=tt;i++)
if(T[i]==t)
return(i);
return(-1);
}
char pops2;
struct node1
{
char s2;int s1;
};
struct node1 stack[10];
int pops1,top=0;
void parser(void)
{
int r,c;
struct t lr[10];
char t,acc='f',str[10];
cout<<"Enter I/p String To Parse: ";
cin>>str;
strcat(str,"$");
stack[0].s1=0;
stack[0].s2='\n';
cout<<"\n\n STACK";
cout<<"\t\t INPUT";
cout<<"\t\t ACTION";
cout<<"\n =====";
cout<<"\t\t =======";
cout<<"\t\t =======";
i=0;
cout<<"\n";
cout<<stack[top].s1;
cout<<" \t\t\t ";
for(int j=0;j<strlen(str);j++)
cout<<str[j];
do
{
r=stack[top].s1;
c=find_index(str[i]);
if(c==-1)
cout<<"\n Error! Invalid String!";
return;
}
while(top!=0);
switch(action[r],lr[c].s)
{
case 'S':
{
push(str[i],action[r].lr[c].n);
i++;
cout<<"\t\t\t Shift";
break;
}
case 'R':
{
t=prod[action[r].lr[c].n][3];
do
{
pop();
}
while(pops2!=t);
t=prod[action[r].lr[c].n][0];
r=stack[top].s1;
c=find_index(t);
push(t,action[r].gr[c-tt-1]);
cout<<"\t\t\t Reduce";
break;
}
case 'A':
{
cout<<"\t\t\t Accept";
cout<<"\n\n\n String accepted";
acc='t';
getch();
return;
}
default:
{
cout<<"\n\n\n Error! String not accepted!";
getch();
exit(0);
}
}
for(j=0;j<=top;j++)
cout<<stack[j].s2<<stack[j].s1;
if(top<4)
cout<<"\t\t\t";
else
cout<<"\t\t";
for(j=i;j<strlen(str);j++)
cout<<str[j];
if(acc=='t')
return;
}
int find_index(char temp)
{
for(int i=0;i<=tt+tnt;i++)
{
if(i<=tt)
{
if(T[i]==temp)
return(i);
}
else
if(NT[i-tt-1]==temp)
return(i);
}
return(-1);
}
void push(char t2,int t1)
{
++top;
stack[top].s1=t1;
stack[top].s2=t2;
return;
}
void pop(void)
{
pops1=stack[top].s1;
pops2=stack[top].s2;
--top;
return;
}
Back to top
