pipe; fork

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>


int main (void)  
{
  int fd1[2] ; // Pipe1   fd[0] = read,   fd[1]=write
  int fd2[2] ; // Pipe2   fd[0] = read,   fd[1]=write

  char buf[100], buf_zahl1[50], buf_zahl2[50], rz[2];
  int n=0;


  int ergebnis=0, zahl1=0, zahl2=0;                    // Variable


  pid_t ForkPID ;


  if (pipe(fd1) < 0) 
    {
      printf("Pipe1 creation failed ...\n") ;
      exit(1) ;
     }

  if (pipe(fd2) < 0) 
    {
      printf("Pipe1 creation failed ...\n") ;
      exit(1) ;
     }


  if ((ForkPID=fork()) < 0) 
    {
      printf("Fork failed ...\n") ;
      exit(1) ;
     }


  if (ForkPID == 0)                             // THE CHILD
    {
      close(fd1[1]) ; // close write port --> read
      close(fd2[0]) ; // close read port  --> write

         n = read(fd1[0],buf_zahl1,sizeof(buf_zahl1));  // einlesen des gesendeten vom Parent
 buf_zahl1[n]=(char)NULL;                       // Nullterminierung

 n = read(fd1[0],rz,sizeof(rz));
 rz[n]=(char)NULL;


 n = read(fd1[0],buf_zahl2,sizeof(buf_zahl2));
 buf_zahl2[n]=(char)NULL;


 
 zahl1= atoi(buf_zahl1);
zahl2= atoi(buf_zahl2);


 if (rz[0] == '+')
           {
    ergebnis= zahl1 + zahl2;
   }
         if (rz[0]== '-')
   {
    ergebnis= zahl1 - zahl2;   
   }
 
 if (rz[0]== '*')
   {
    ergebnis= zahl1 * zahl2;   
   }


 if (rz[0]== '/')
   {
    ergebnis= zahl1 / zahl2;   
   }


 sprintf (buf, "Ergebnis= %d\n",ergebnis);
// write (STDOUT_FILENO, buf , strlen(buf));
 n = write (fd2[1],buf,strlen(buf));
         printf ("n= %d\n",n);
     } 


  else                                          // THE PARENT
    { 
      close(fd1[0]) ; // close read port  --> write
      close(fd2[1]) ; // close write port --> read

       char *Buffer= "Zahl 1 = "; 
       char *Buffer1= "Rechenzeichen= ";
       char *Buffer2= "Zahl 2 = ";

         write (STDOUT_FILENO, Buffer, strlen(Buffer));
         n = read (STDIN_FILENO,buf_zahl1,sizeof(buf_zahl1));
 buf_zahl1[n]=(char)NULL;
 write (fd1[1],buf_zahl1,strlen(buf_zahl1));
 
 write (STDOUT_FILENO, Buffer1, strlen(Buffer1));
 n = read (STDIN_FILENO,rz,sizeof(rz));
 rz[n]=(char)NULL;
 write (fd1[1],rz,strlen(rz));
 
         write (STDOUT_FILENO, Buffer2, strlen(Buffer2));
 n = read (STDIN_FILENO,buf_zahl2,sizeof(buf_zahl2));
 buf_zahl2[n]=(char)NULL;
 write (fd1[1],buf_zahl2,strlen(buf_zahl2));

 n = read(fd2[0],buf,sizeof(buf));
 printf ("n1= %d\n",n);
 buf[n]='\0';
 write(STDOUT_FILENO,buf,strlen(buf));

 
     }


  return(0);

}