C PROGRAM FOR COMPUTATION OF FIRST

ALGORITHM

To compute FIRST(X) for all grammar symbols x, apply the following rules until no more terminals can be

added to any FIRST set.

1.  if X is terminal, then FIRST(X) is {X}.

2.  if X is nonterminal and X-> aα is a production, then add a to FIRST(X). if X->€ to FIRST(X)

3.  if -> Y1,Y2,…….Yk is a production, then for all i such that all of Y1,….Yi-1 are nonterminals and FIRST(Yj) contains €  for j=1,2,…… i-1, add every non-€ symbol in FIRST(Y1) to FIRST(x). if V is in FIRST(Yj) for j=1,2,………k, then add € to FIRST(X).

PROGRAM FOR COMPUTATION OF FIRST

#include<stdio.h>

#include<conio.h>

#include<string.h>

void main()

{

char t[5],nt[10],p[5][5],first[5][5],temp;

int i,j,not,nont,k=0,f=0;

clrscr();

printf("\nEnter the no. of Non-terminals in the grammer:");

scanf("%d",&nont);

printf("\nEnter the Non-terminals in the grammer:\n");

for(i=0;i<nont;i++)

{

scanf("\n%c",&nt[i]);

}

printf("\nEnter the no. of Terminals in the grammer: ( Enter e for absiline ) ");

scanf("%d",&not);

printf("\nEnter the Terminals in the grammer:\n");

for(i=0;i<not||t[i]=='$';i++)

{

scanf("\n%c",&t[i]);

}

for(i=0;i<nont;i++)

{

p[i][0]=nt[i];

first[i][0]=nt[i];

}

printf("\nEnter the productions :\n");

for(i=0;i<nont;i++)

{

scanf("%c",&temp);

printf("\nEnter the production for %c ( End the production with '$' sign ) :",p[i][0]);

for(j=0;p[i][j]!='$';)

{

j+=1;

scanf("%c",&p[i][j]);

}

}

for(i=0;i<nont;i++)

{

printf("\nThe production for %c -> ",p[i][0]);

for(j=1;p[i][j]!='$';j++)

{

printf("%c",p[i][j]);

}

}

for(i=0;i<nont;i++)

{

f=0;

for(j=1;p[i][j]!='$';j++)

{

for(k=0;k<not;k++)

{

if(f==1)

break;

if(p[i][j]==t[k])

{

first[i][j]=t[k]; first[i][j+1]='$'; f=1;

break;

}

else if(p[i][j]==nt[k])

{

first[i][j]=first[k][j];

if(first[i][j]=='e')

continue; first[i][j+1]='$'; f=1;

break;

}

}

}

}

for(i=0;i<nont;i++)

{

printf("\n\nThe first of %c -> ",first[i][0]);

for(j=1;first[i][j]!='$';j++)

{

}

}

getch();

}

printf("%c\t",first[i][j]);

OUTPUT

Enter the no. of Non-terminals in the grammer:3

Enter the Non-terminals in the grammer: ERT

Enter the no. of Terminals in the grammer: ( Enter e for absiline ) 5

Enter the Terminals in the grammer:

ase*+

Enter the productions :

Enter the production for E ( End the production with '$' sign ) :a+s$ Enter the production for R ( End the production with '$' sign ) :e$ Enter the production for T ( End the production with '$' sign ) :Rs$ The production for E -> a+s

The production for R -> e

The production for T -> Rs

The first of E -> a

The first of R -> e

The first of T -> e     s

Posted in: C / C++ Program