LOGIC: 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).
#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",¬);
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++)
{
printf("%c\t",first[i][j]);
}
}
getch();
}
INPUT/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</nont;i++)<></not;k++)<></nont;i++)<></nont;i++)<></nont;i++)<></nont;i++)<></not||t[i]=='$';i++)<></nont;i++)<>