Uppercase letter using pipe in C - c

Question

#include <stdio.h>
#include <ctype.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <termios.h>
static struct termios old, new;
/* Initialize new terminal i/o settings */
void initTermios(int echo)
{
tcgetattr(0, &old); /* grab old terminal i/o settings */
new = old; /* make new settings same as old settings */
new.c_lflag &= ~ICANON; /* disable buffered i/o */
new.c_lflag &= echo ? ECHO : ~ECHO; /* set echo mode */
tcsetattr(0, TCSANOW, &new); /* use these new terminal i/o settings now */
}
/* Restore old terminal i/o settings */
void resetTermios(void)
{
tcsetattr(0, TCSANOW, &old);
}
/* Read 1 character - echo defines echo mode */
char getch_(int echo)
{
char ch;
initTermios(echo);
ch = getchar();
resetTermios();
return ch;
}
/* Read 1 character without echo */
char getch(void)
{
return getch_(0);
}
/* Read 1 character with echo */
char getche(void)
{
return getch_(1);
}
void INThandler(int);
void INThandler(int sig)
{
char c;
signal(sig, SIG_IGN);
printf("\n Ctrl+c foi detetado, clique y para confirmar \n");
c = getchar();
if(c == 'y' || c == 'Y')
exit(0);
else
signal(SIGINT, INThandler);
getchar();
}
int main()
{
signal(SIGINT, INThandler);
int fd[2];
char readbuffer[80];
pipe(fd);
int pid = fork();
char ch;
if(pid < 0)
{
printf("\n Erro");
exit(1);
}
else if(pid == 0)
{
close(fd[0]);
do
{
ch = getch();
write(fd[1], &ch, sizeof(ch));
} while(ch != '\n');
getchar();
}
else
{
close(fd[1]);
while(1)
{
read(fd[0], readbuffer, sizeof(readbuffer));
char upper = toupper(readbuffer[0]);
char down = tolower(readbuffer[0]);
if(readbuffer[0] != upper)
{
printf("%c \n", upper);
}
else
{
printf("%c \n", down);
}
}
}
return(0);
}
So basically this is a task that is: Using communication between processes, convert automatically upper letters to small letters, and small letters to upper letters, without them appearing in input. Basically I don't see my input just the output. And when CTRL+C is hit, the program should recognize it and ask for a confirmation by asking the user to type "y".
My program runs, but when I remove the \n from "printf("%c \n", upper);" and from "printf("%c \n", down);" the program starts acting weird... When I remove it I have to hit enter to see the output, but with it it appears automatically just like I wanted... Can someone explain me why?
I am using ubuntu.

Answer 1

printf doesn't actually print to stdout immediately -- it just puts characters into an output buffer to be flushed to stdout at some later point. That "later point" is generally whenever a newline is printed if the output is a terminal, but you can change that with setbuf:
setbuf(stdout, 0); // set stdout to unbuffered
after which every call to printf will immediately flush the buffer. Alternately, you can use fflush(stdout) to flush the buffer at any specific point in your program.