Programming

int main(int argc, char* argv[])
{
        int tubo1[2], tubo2[2], i,num_proc=0,numero=0,longitud=0,pid=0;
        char frase[MAXNAME];
      
        ...

        pipe(tubo1);

        dup2(tubo1[0],tubo2[0]);
        dup2(tubo1[1],tubo2[1]);

        close(tubo1[0]);
        close(tubo1[1]);


        /* Creating num_proc number of processes */

        for( i=0; i<num_proc; i++)
        {
                pipe(tubo1);

                if ( (pid=fork()) == -1 )
                        printf("\nError. Fork\n\n");
                else
                {
                        if ( pid )
                        {
                                /* Father´s code */

                                dup2(tubo1[0],tubo2[0]);
                                close(tubo1[0]);
                                close(tubo1[1]);
                        }
                        else
                        {
                                dup2(tubo1[1],tubo2[1]);
                                close(tubo1[0]);
                                close(tubo1[1]);
                                break;
                        }
                }
        }


        if ( pid )
        {
                /* Father */

                for (i=0; i<2; i++)
                {
                        /* "frase" modification. Father starts. */

                        write(tubo2[1], frase, longitud*sizeof(char));
                        read(tubo2[0], frase, longitud*sizeof(char));
                }
        }
        else
        {
                /* Children code */
                for (i=0; i<2; i++)
                {
                        read(tubo2[0], frase, MAXNAME*sizeof(char))
                        /* "frase" modification */
                        write(tubo2[1], frase, longitud*sizeof(char));
                }
        }

 return 0;
}

...
if (pid)
{
       /* father */
       printf("\nhello..."); /* this line is only an example. 
                                      the program executes it. Everything ok..*/
       for(i=0; i<2; i++)  /* it doest go into this loop. why?! */
       {
                /* modification of "frase" */
                ...
        }
}
else
{
         read(...); /* the function returns -1. Error */
         ...
}