[c] Catch Ctrl-C in C

@Peter Varo updated Dirk's answer, but Dirk rejected the change. Here's the new answer by Peter:

Although the above snippet is a correct example, one should use the more modern types and guarantees provided by the later standards if possible. Therefore, here is a safer and modern alternative for those who are seeking for the and conforming implementation:

#include <signal.h>
#include <stdlib.h>
#include <stdio.h>

static volatile sig_atomic_t keep_running = 1;

static void sig_handler(int _)
{
    (void)_;
    keep_running = 0;
}

int main(void)
{
    signal(SIGINT, sig_handler);

    while (keep_running)
        puts("Still running...");

    puts("Stopped by signal `SIGINT'");
    return EXIT_SUCCESS;
}

C11 Standard: 7.14§2 The header <signal.h> declare a type ... sig_atomic_t which is the (possibly volatile-qualified) integer type of an object that can be accessed as an atomic entity, even in the presence of asynchronous interrupts.

Furthermore:

C11 Standard: 7.14.1.1§5 If the signal occurs other than as the result of calling the abort or raise function, the behavior is undefined if the signal handler refers to any object with static or thread storage duration that is not a lock-free atomic object other than by assigning a value to an object declared as volatile sig_atomic_t...