c program for dfa (deterministic finite automata). Let us first know what is DFA or let us again revise the concept of DFA? Automation are basically language acceptor or language recognizer. A finite automata is a collection of 5-tuple(Q,∑,∂,q0,F). Where
Q=finite set of states
∑=input symbol
∂=transition function
q0=initial state
F=set of final state

c program for dfa

#include<stdio.h>
#include<conio.h>

int ninputs;

int check(char,int ); //function declaration
int dfa[10][10];
char c[10], string[10];

int main()
{
     int nstates, nfinals;
     int f[10];
     int i,j,s=0,final=0;
     printf("enter the number of states that your dfa consist of \n");
     scanf("%d",&nstates);
     printf("enter the number of input symbol that dfa have \n");
     scanf("%d",&ninputs);
     printf("\nenter input symbols\t");

     for(i=0; i<ninputs; i++)
     {
           printf("\n\n %d input\t", i+1);
           printf("%c",c[i]=getch());
     }

     printf("\n\nenter number of final states\t");
     scanf("%d",&nfinals);

     for(i=0;i<nfinals;i++)
     {
          printf("\n\nFinal state %d : q",i+1);
          scanf("%d",&f[i]);
     }

     printf("-----------------------------------------------------------------------");
     printf("\n\ndefine transition rule as (initial state, input symbol ) = final state\n");

     for(i=0; i<ninputs; i++)
     {
          for(j=0; j<nstates; j++)
          {
               printf("\n(q%d , %c ) = q",j,c[i]);
               scanf("%d",&dfa[i][j]);
          }
     }

     do
     {
          i=0;
          printf("\n\nEnter Input String.. ");
          scanf("%s",string);

          while(string[i]!='\0')
          if((s=check(string[i++],s))<0)
          break;
          for(i=0 ;i<nfinals ;i++)
          if(f[i] ==s )
          final=1;
          if(final==1)
          printf("\n valid string");
          else
          printf("invalid string");
          getch();

          printf("\nDo you want to continue.?  \n(y/n) ");
     }
     while(getch()=='y');

     getch();
}
int check(char b,int d)
{
     int j;
     for(j=0; j<ninputs; j++)
     if(b==c[j])
     return(dfa[d][j]);
     return -1;
}