Creating a frontend for bc

FILE *bc_read;
  int bytes_read;
  size_t nbytes = 100;
  char *my_string;

   bc_read = popen ("bc -q /tmp/expression", "r");
 
 
  if ((!bc_read) )
    {
      cout <<   "Pipe failed.\n" << endl;
      return EXIT_FAILURE;
    }
    
  my_string = (char *) malloc (nbytes );
  bytes_read = getline (&my_string, &nbytes,bc_read);
  
  if (pclose (bc_read) != 0)
    {
              cout <<  "Error.\n" << endl;
    }
  
  cout << my_string;

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <wait.h>

/* bcfe -- bc front end
	Create a process running bc and send commands and read responses
	via pipes.
*/

int main(void) 
{
	char buf[64]; 
	int wrpipe[2];	// two file descriptors:
	int rdpipe[2]; 	//   [0] read, [1] write
	int pid;

	// open the two pipes
	// note that a single pipe should not be used for bidirectional
	//  communication, so we open one to write to and one to read from.
	if (pipe(wrpipe) == -1) 
	{
		perror("wrpipe error"); 
		exit(-1);
	}
	if (pipe(rdpipe) == -1) 
	{
		perror("rdpipe error"); 
		exit(-1);
	}

	// fork a child process
	pid = fork( );
	if (pid == -1) 
	{
		perror("fork error"); 
		exit(-1);
	}

	// initialize the buffer
        memset(buf,0,64);

	// different actions for child and parent
	if (pid == 0) 
	{	// child
		// perform redirection 
		// close stdin & stdout then dup pipes to them
		close(0);    	// close stdin
		dup2(wrpipe[0],0);
		close(1);	// close stdout
		dup2(rdpipe[1],1);

		// close our end of the pipes
		close(wrpipe[0]);	// write pipe
		close(wrpipe[1]);	// write pipe
		close(rdpipe[0]);	// read pipe
		close(rdpipe[1]);	// read pipe

		// run bc
		// this replaces the child process, but keeps its file descriptors
		execlp("bc","bc",0);

		// will never reach here
	}
	else 
	{	// parent
		// close the read-end of the write pipe and
		// the write-end of the read pipe
		close(wrpipe[0]);	// write pipe
		close(rdpipe[1]);	// read pipe

		// send a problem to bc
		write(wrpipe[1],"1+1\n",4);

		// read bc's answer and echo it to stdout
		read(rdpipe[0],buf,64);
		printf("%s\n",buf);

		// command bc to quit
		write(wrpipe[1],"quit\n",5);

		// wait for bc to terminate
		waitpid(pid,NULL,0);

		// close the pipes
		close(wrpipe[1]);	// write pipe
		close(rdpipe[0]);	// read pipe
	}
    return 0;
}