120. Convert Integer to Hex String Without sprintf or itoa functions

In embedded systems, you may need to transmit an integer value as a hexadecimal string over UART, display, or logs — but without using heavy standard functions like sprintf() or itoa().

Your task is to:

• Read an unsigned 16-bit integer num
• Print its hexadecimal string representation in uppercase
• Do not use any built-in conversion functions like itoa(), sprintf(), etc.

Example-1

Input: 255
Output: FF

Example-2

Input: 4095
Output: FFF

Example-3

Input: 0
Output: 0

Example-4

Input: 4660
Output: 1234