Calculation of First and Follow programs for Compiler Design Lab

Simulate First and Follow of a Grammar

First.c :

/*Assumptions:

Each Non terminal character is represented by one Uppercase letter.

Each Terminal character is represented by one lowercase letter.

LHS and RHS of each production will be separated by a "=" symbol.

There will be no Blank space within a production string. 

Assumed that Left recursion is avoided in all input productions. 

Use $ to represent epsilon  */

#include<stdio.h>

#include<ctype.h>

void FIRST(char[],char );

void addToResultSet(char[],char);

int numOfProductions;

char productionSet[10][10];

main()

{

    int i;

    char choice;

    char c;

    char result[20];

    printf("How many number of productions ? :");

    scanf(" %d",&numOfProductions);

    for(i=0;i<numOfProductions;i++)/*read production string eg: E=E+T*/

    {

        printf("Enter productions Number %d : ",i+1);

        scanf(" %s",productionSet[i]);

    }

    do

    {

        printf("\n Find the FIRST of  :");

        scanf(" %c",&c);

FIRST(result,c); /*Compute FIRST; Get Answer in 'result' array*/

        printf("\n FIRST(%c)= { ",c);

        for(i=0;result[i]!='\0';i++)

printf(" %c ",result[i]);       /*Display result*/

        printf("}\n");

         printf("press 'y' to continue : ");

        scanf(" %c",&choice);

    }

    while(choice=='y'||choice =='Y');

}

/*

 *Function FIRST:

 *Compute the elements in FIRST(c) and write them

 *in Result Array.

 */

void FIRST(char* Result,char c)

{

    int i,j,k;

    char subResult[20];

    int foundEpsilon;

    subResult[0]='\0';

    Result[0]='\0';

    /*If X is terminal, FIRST(X) = {X}.*/

    if(!(isupper(c)))

    {

        addToResultSet(Result,c);

               return ;

    }

    /*If X is non terminal

    /Read each production*/

    for(i=0;i<numOfProductions;i++)

    {

/*Find production with X as LHS*/

        if(productionSet[i][0]==c)

        {

/*If X =e is a production, then add e to FIRST(X).*/

 if(productionSet[i][2]=='#') addToResultSet(Result,'#');

   /*If X is a non-terminal, and X = Y1 Y2 … Yk

            is a production, then add a to FIRST(X)

            if for some i, a is in FIRST(Yi),

   and e is in all of FIRST(Y1), …, FIRST(Yi-1).*/

      else

            {

                j=2;

                while(productionSet[i][j]!='\0')

                {

                foundEpsilon=0;

                FIRST(subResult,productionSet[i][j]);

                for(k=0;subResult[k]!='\0';k++)

                    addToResultSet(Result,subResult[k]);

                 for(k=0;subResult[k]!='\0';k++)

                     if(subResult[k]=='#')

                     {

                         foundEpsilon=1;

                         break;

                     }

/*No e found, no need to check next element*/

                 if(!foundEpsilon)

                     break;

                 j++;

                }

            }

    }

}

    return ;

}

/* addToResultSet adds the computed

 *element to result set.

 *This code avoids multiple inclusion of elements

  */

void addToResultSet(char Result[],char val)

{

    int k;

    for(k=0 ;Result[k]!='\0';k++)

        if(Result[k]==val)

            return;

    Result[k]=val;

    Result[k+1]='\0';

}

Output:

Follow.c 

#include<stdio.h>
#include<ctype.h>
#include<string.h>
int n,m=0,p,i=0,j=0;
char a[10][10],followResult[10];
void follow(char c);
void first(char c);
void addToResult(char);
int main()
{
 int i;
 int choice;
 char c,ch;
 clrscr();
 printf("Enter the no.of productions: ");
scanf("%d", &n);
 printf(" Enter %d productions\nProduction with multiple terms should be give as separate productions \n", n);
 for(i=0;i<n;i++)
  scanf("%s%c",a[i],&ch);
    do
 {
  m=0;
  printf("Find FOLLOW of -->");
  scanf(" %c",&c);
  follow(c);
  printf("FOLLOW(%c) = { ",c);
  for(i=0;i<m;i++)
   printf("%c ",followResult[i]);
  printf(" }\n");
  printf("Do you want to continue(Press 1 to continue....)?");
 scanf("%d",&choice);
 }
 while(choice==1);
}
void follow(char c)
{
    if(a[0][0]==c)addToResult('$');
 for(i=0;i<n;i++)
 {
  for(j=2;j<strlen(a[i]);j++)
  {
   if(a[i][j]==c)
   {
    if(a[i][j+1]!='\0')first(a[i][j+1]);
    if(a[i][j+1]=='\0'&&c!=a[i][0])
     follow(a[i][0]);
   }
  }
 }
}
void first(char c)
{
      int k;
                 if(!(isupper(c)))
    /*f[m++]=c;  */
                     addToResult(c);
                 for(k=0;k<n;k++)
                 {
                 if(a[k][0]==c)
                 {
                 if(a[k][2]=='#') follow(a[i][0]);
                 else if(islower(a[k][2]))
    /*f[m++]=a[k][2];    */
                     addToResult(a[k][2]);
                 else first(a[k][2]);
                 }
                 }
}
void  addToResult(char c)
{
    int i;
    for( i=0;i<=m;i++)
        if(followResult[i]==c)
            return;
   followResult[m++]=c;
}

Output: