Making Errors and Learning...in C/C++?

/usr/bin/ld: /tmp/ccK4sGN3.o: in function `main':
OutputGPIO.c:(.text+0x20): undefined reference to `gpio_open'
/usr/bin/ld: OutputGPIO.c:(.text+0x42): undefined reference to `gpio_write'
/usr/bin/ld: OutputGPIO.c:(.text+0x4e): undefined reference to `gpio_set_direction_output'
/usr/bin/ld: OutputGPIO.c:(.text+0x64): undefined reference to `gpio_close'
collect2: error: ld returned 1 exit status

# FROM

// basic example for handling input change events

#include "sysfs-gpio.h"
#include <stdio.h>

int main()
{
        struct Gpio gpio = GPIO_INITIALIZER;
        gpio_open( &gpio, "/sys/class/gpio/gpio51", GPIO_RDWR );

        int const timeout_ms = 3000;  // -1 = no timeout

        if ( gpio_open_output ) {
                printf( "%d\n", &gpio);
                gpio_write( &gpio, 0 );
                gpio_set_direction_output(&gpio, 1);
        }
        else {
                ( ( &gpio, timeout_ms ) );
        }
        printf( "The LED!\n", timeout_ms );

        gpio_close( &gpio );
        return 0;
}