Basic program to run TM1637 Four Digit Display with nRF52840 DK

I have controlled an LED with a push button connected to GPIO pins P0.03, P0.04 respectively.Now I want to use those pins as CLK and DIO pins of TM1637 Display.I wrote a basic program to control that display as follows:

#include <zephyr.h>
#include <device.h>
#include <devicetree.h>
#include <drivers/gpio.h>
#include <sys/printk.h>

#define SLEEP_TIME_MS 10
// Defining GPIO pins
#define CLK_NODE DT_ALIAS(gpiocus0)

#if DT_NODE_HAS_STATUS(CLK_NODE, okay)
#define CLK DT_GPIO_LABEL(CLK_NODE, gpios)
#define CLK_PIN DT_GPIO_PIN(CLK_NODE, gpios)
#define CLK_FLAGS DT_GPIO_FLAGS(CLK_NODE, gpios)
#else
#error "Unsupported board: gpio22 devicetree alias is not defined"
#endif

#define DIO_NODE DT_ALIAS(gpiocus1)

#if DT_NODE_HAS_STATUS(DIO_NODE, okay)
#define DIO DT_GPIO_LABEL(DIO_NODE, gpios)
#define DIO_PIN DT_GPIO_PIN(DIO_NODE, gpios)
#define DIO_FLAGS DT_GPIO_FLAGS(DIO_NODE, gpios)
#else
#error "Unsupported board: gpio24 devicetree alias is not defined"
#endif


const struct device *dev;

void writeByte(uint8_t wr_data);

/**
 * @brief Function for application main entry.
 */
void main(void)
{
	printk("Blink LED \n\r");
	
	int ret;

	dev = device_get_binding(CLK);
    if (dev == NULL) 
    {
        return;
    }
    
    ret = gpio_pin_configure(dev, CLK_PIN, GPIO_OUTPUT_ACTIVE | CLK_FLAGS);
    if (ret < 0) 
    {
        return;
    }

    ret = gpio_pin_configure(dev, DIO_PIN, GPIO_OUTPUT_ACTIVE | DIO_FLAGS);
	if (ret < 0)
	{
		return;
	}
    
	writeByte(0x08);

}
/** @} */

void writeByte(uint8_t wr_data)
{
	uint8_t i;
	for (i = 0; i < 8; i++) // sent 8bit data
	{
		gpio_pin_set(dev, CLK_PIN, 0);
		if (wr_data & 0x01)
		{
			gpio_pin_set(dev, DIO_PIN, 1);
		}
		else
		{
			gpio_pin_set(dev, DIO_PIN, 0);
		}
		wr_data >>= 1;
		gpio_pin_set(dev, CLK_PIN, 1);
	}
	printk("Data : %d",wr_data);
}

The device tree overlay file is given as : 

// To get started, press Ctrl+Space to bring up the completion menu and view the available nodes.
// For more help, browse the DeviceTree documentation at https://docs.zephyrproject.org/latest/guides/dts/index.html

/ {
    gpiocustom {
        compatible = "gpio-keys";
        gpiocus0: gpiocus_0 {
            gpios = <&gpio0 3 GPIO_ACTIVE_LOW>;
            label = "Custom gpio 3";
        };
        gpiocus1: gpiocus_1 {
            gpios = <&gpio0 4 GPIO_ACTIVE_LOW>;
            label = "Custom gpio 4";
        };
    };
    aliases {
        gpiocus0 = &gpiocus0;
        gpiocus1 = &gpiocus1;
    };
};

On building this code, I won't get any error. It build successfully. When I flash that to my nRF52840 DK with TM1637 Display connected to the GPIO pins , I won't get any output on the Display. I don't know what I am missing. Please guide me to get the display working for my DK.

Reference:

TM1637 Display program from Devzone.

I modified the code mentioned by an Nordic Engineer in the above mentioned link, to the current data types and device trees.

Hardware : 

nRF52840 DK - 1

TM1637 Four Digit Seven Segment Display - 1

Software : 

VS Code with nRF Connect Extension 

nRF Connect SDk - v 1.9.1

nRf Connect Toolchain - v 1.9.1

Questions: 

1) Is the C program to control the display is correct or not ?

2) I am able to declare only the analog pins (Pin No : 3, 4, 28, 29, 30, 31) led and push button. Other than that , I won't be able to declare other GPIO pins for even Blink example. How can I use other GPIO pins for my purposes ?

Please reply as soon as possible.

Thankyou.

-Vicky