Raspberry Pi - detect button press

button.c

// button.c
// gcc -o button button.c -l bcm2835 
// run as root
// sudo ./button

#include <bcm2835.h>
#include <stdio.h>

// Input on RPi pin GPIO 15
#define PIN RPI_GPIO_P1_15

int main(int argc, char **argv)
{

    if (!bcm2835_init())
        return 1;

    // Set PIN to be an input
    bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_INPT);
    //  add a pullup
    bcm2835_gpio_set_pud(PIN, BCM2835_GPIO_PUD_UP);
    // and enble low
    bcm2835_gpio_len(PIN);

    while (1)
    {
        if (bcm2835_gpio_eds(PIN))
        {
            // Now clear the eds flag by setting it to 1
            bcm2835_gpio_set_eds(PIN);
            printf("Button Pressed!\n");
        }
        delay(500);
    }
    bcm2835_close();
    return 0;
}