Answer:
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<string.h>
#include<pthread.h>
//#include<sys/wait.h>
int main(int argc, char** argv)
{
int fd1[2];
int fd2[2];
int fd3[2];
int fd4[2];
char message[] = "abcd";
char input_str[100];
pid_t p,q;
if (pipe(fd1)==-1)
{
fprintf(stderr, "Pipe Failed" );
return 1;
}
if (pipe(fd2)==-1)
{
fprintf(stderr, "Pipe Failed" );
return 1;
}
if (pipe(fd3)==-1)
{
fprintf(stderr, "Pipe Failed" );
return 1;
}
if (pipe(fd4)==-1)
{
fprintf(stderr, "Pipe Failed" );
return 1;
}
p = fork();
if (p < 0)
{
fprintf(stderr, "fork Failed" );
return 1;
}
// child process-1
else if (p == 0)
{
close(fd1[0]);// Close reading end of first pipe
char concat_str[100];
printf("\n\tEnter meaaage:"):
scanf("%s",concat_str);
write(fd1[1], concat_str, strlen(concat_str)+1);
// Concatenate a fixed string with it
int k = strlen(concat_str);
int i;
for (i=0; i<strlen(fixed_str); i++)
{
concat_str[k++] = fixed_str[i];
}
concat_str[k] = '\0';//string ends with '\0'
// Close both writting ends
close(fd1[1]);
wait(NULL);
//.......................................................................
close(fd2[1]);
read(fd2[0], concat_str, 100);
if(strcmp(concat_str,"invalid")==0)
{
printf("\n\tmessage not send");
}
else
{
printf("\n\tmessage send to prog_2(child_2).");
}
close(fd2[0]);//close reading end of pipe 2
exit(0);
}
else
{
close(fd1[1]);//Close writting end of first pipe
char concat_str[100];
read(fd1[0], concal_str, strlen(concat_str)+1);
close(fd1[0]);
close(fd2[0]);//Close writing end of second pipe
if(/*check if msg is valid or not*/)
{
//if not then
write(fd2[1], "invalid",sizeof(concat_str));
return 0;
}
else
{
//if yes then
write(fd2[1], "valid",sizeof(concat_str));
close(fd2[1]);
q=fork();//create chile process 2
if(q>0)
{
close(fd3[0]);/*close read head offd3[] */
write(fd3[1],concat_str,sizeof(concat_str);//write message by monitor(main process) using fd3[1]
close(fd3[1]);
wait(NULL);//wait till child_process_2 send ACK
//...........................................................
close(fd4[1]);
read(fd4[0],concat_str,100);
close(fd4[0]);
if(sctcmp(concat_str,"ack")==0)
{
printf("Messageof child process_1 is received by child process_2");
}
else
{
printf("Messageof child process_1 is not received by child process_2");
}
}
else
{
if(p<0)
{
printf("Chiile_Procrss_2 not cheated");
}
else
{
close(fd3[1]);//Close writing end of first pipe
char concat_str[100];
read(fd3[0], concal_str, strlen(concat_str)+1);
close(fd3[0]);
close(fd4[0]);//Close writing end of second pipe
write(fd4[1], "ack",sizeof(concat_str));
}
}
}
close(fd2[1]);
}
}
and y = a. If i = 1, we must have j = k and adding any number of a’s still preserves the membership in the language. For i > 2, all strings obtained by pumping y as defined above, have two or more a’s and hence are always in the language.