first and follow

 Ex-6  Write a C program to compute the First and Follow sets for the given Grammar 

/* A=aAbA 

B=bBaB 

A=a 

B=b   */ 

 

 

#include<stdio.h> 

#include<math.h> 

#include<string.h> 

#include<ctype.h> 

#include<stdlib.h> 

int n,m=0,p,i=0,j=0; 

char a[10][10],f[10]; 

void follow(char c); 

void first(char c); 

int main(){ 

int i,z; 

char c,ch; 

printf("Enter the no of prooductions:\n"); 

scanf("%d",&n); 

printf("Enter the productions:\n"); 

for(i=0;i<n;i++) 

scanf("%s%c",a[i],&ch); 

do{ 

m=0; 

printf("Enter the elemets whose fisrt & follow is to be found:"); 

scanf("%c",&c); 

first(c); 

printf("First(%c)={",c); 

for(i=0;i<m;i++) 

printf("%c",f[i]); 

printf("}\n"); 

strcpy(f," "); 

//flushall(); 

m=0; 

follow(c); 

printf("Follow(%c)={",c); 

for(i=0;i<m;i++) 

printf("%c",f[i]); 

printf("}\n"); 

printf("Continue(0/1)?"); 

scanf("%d%c",&z,&ch); 

}while(z==1); 

return(0); 

} 

void first(char c) 

{ 

int k; 

if(!isupper(c)) 

f[m++]=c; 

for(k=0;k<n;k++) 

{ 

if(a[k][0]==c) 

{ 

if(a[k][2]=='$') 

follow(a[k][0]); 

else if(islower(a[k][2])) 

f[m++]=a[k][2]; 

else first(a[k][2]); 

} 

} 

} 

void follow(char c) 

{ 

if(a[0][0]==c) 

f[m++]='$'; 

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]); 

} 

} 

} 

}