Wait only 5 second for user input - c

Question

I want to write a simple c program in turbo c++ 4.5 editor such that in only wait 5 seconds for user input. As an example,
#include <stdio.h>
void main()
{
int value = 0;
printf("Enter a non-zero number: ");
// wait only 5 seconds for user input
scanf("%d",&value);
if(value != 0) {
printf("User input a number");
} else {
printf("User dont give input");
}
}
So, what will be the code for 5 seconds wait for 'scanf' functionality and otherwise execute if-else part.

Answer 1

Try a select(2) loop: https://www.mirbsd.org/man2/select on stdin (fd#0) with a timeout of 5 seconds; run the scanf(3) only if select returns indicating there is data. (See the c_read() function in the mksh source code for an example.)
Other functions, like poll(2), are also possible. Nonblocking I/O is a bit overkill.
OK, here’s a working (on MirBSD) example using select:
#include <sys/types.h>
#include <sys/time.h>
#include <err.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
int
main(void)
{
int value = 0;
struct timeval tmo;
fd_set readfds;
printf("Enter a non-zero number: ");
fflush(stdout);
/* wait only 5 seconds for user input */
FD_ZERO(&readfds);
FD_SET(0, &readfds);
tmo.tv_sec = 5;
tmo.tv_usec = 0;
switch (select(1, &readfds, NULL, NULL, &tmo)) {
case -1:
err(1, "select");
break;
case 0:
printf("User dont give input");
return (1);
}
scanf("%d", &value);
if (value != 0) {
printf("User input a number");
} else {
printf("User dont give input");
}
return (0);
}
You might want to play with the exit codes a bit and sprinkle a few \n throughout the code. The fflush(stdout); is important so that the prompt is shown in the first place…

Answer 2

#include <stdio.h>
#include <signal.h>
void handler(int signo)
{
return;
}
int main()
{
int x;
struct sigaction sa;
sa.sa_handler = handler;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
sigaction(SIGALRM, &sa, NULL);
alarm(5);
if (scanf("%d", &x) == 1)
{
printf("%d\n", x);
alarm(0); // cancel the alarm
}
else
{
printf("timedout\n");
}
return 0;
}

Answer 3

well you can use the halfdelay() function from the curses library