Queries on nus_data_send() functionality?

[noob_with_ucontrollers]

Hi, I have a few general questions on nus_data_send(). 

First off, is there another known way of transferring an array/string via ble to the Nordic mobile app other than the NUS service? 

Secondly, does the nus_data_send() function always need an interrupt/event to get called? 

I am starting with the BLE_UART example in Embedded Studio (SDK 15.2). The main program goes into an indefinite for (';;) loop idle state handle after calling advertising_start(). The way I see this is that the chip is continuously in a low power mode and it advertising so it needs an interrupt (GPIO or NUS or UART)  to initiate a data transfer? 

Why does a program including BLE have to move into a low power sleep state? Can I write a custom data send function including the nus_data_send() and call it in the main successfully with the idle_state_mgmt () function running in an infinite loop at the end? Should the data_send() in the below main program work (i.e. be called despite the for(;;) loop after the advertising  )? 

int main(void)
{
    bool erase_bonds;

    // Initialize.
    uart_init();
    log_init();
    timers_init();
    buttons_leds_init(&erase_bonds);
    power_management_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();
    conn_params_init();
    // SPI 
    init_pins(); 

    nrf_delay_ms (10); 
    // initialize the SPI for ADC ADS1220 communication 
    init_spi(); 

    // Start execution.
    printf("\r\nUART started.\r\n");
    NRF_LOG_INFO("Debug logging for UART over RTT started.");
    advertising_start();

    data_send() ; 

   
    for  (;;)
    {
       idle_state_handle(); 
    }
   
   

}

[noob_with_ucontrollers]

I understand that my value is a HEX/int which is why the ASCII characters on screen do not make sense. 
Is the value shown after  "Notification received from..." the original array value? The 0x-FF-FF-FF-FF....? If so I think that may be the right kind of data I'm expecting. 

I still have two questions though? How do I convert my int or hex array to ASCII? Do I have to convert to ASCII or should the  "Notification received from..." part show me my data as it is anyway?  

I tried using defining a char array and sending that array with my HEX data through the ble_nus_string_send() but that gives me an error as well. The program says I am calling ble_nus_string_send() implicitly and that it is an UNDEFINED call. I made sure I am including "string.h" and "stdlib.h".... How can I use the string_send() function accurately? 

[Hung Bui]

Which ble_nus_string_send() are you talking about ? Do you mean ble_nus_data_send() ? 

I am not sure what exactly you want to do . If you want to display the hex value of your data you can follow what we do in the app (the logging "Notification received from... " ) . 

[noob_with_ucontrollers]

The ble_nus_string_send() is a function for sending string data, like data_send() but different in that it's for string values. Since my data is hex I wanted to send it as a string. 

[Hung Bui]

Everything sending over BLE (or any protocol) is converted to byte array. If you send ASCII data, on the other side it will be converted to string inside the UART app.