wiringPi LED blink

wiringPiLedBlink.c

#include <wiringPi.h>
#include <stdlib.h>

const int gpio21 = 21;

int main(int argc, char const* argv[])
{
        if(wiringPiSetupGpio() == -1)
                exit(1);

        pinMode(gpio21, OUTPUT);

        while(1){
                digitalWrite(gpio21, 0);
                delay(100);
                digitalWrite(gpio21, 1);
                delay(100);
        }
        exit(0);
}