39. Safe Callback Invocation

In embedded firmware, optional callback functions are often used to handle events such as sensor data processing.
This problem focuses on safe callback invocation using nullptr.

You are given an input that specifies whether a callback is registered and a sensor value.
Your task is to safely invoke the callback only if it is registered.

Input Format:

flag value

• flag (integer)
  • 0 → No callback is registered
  • 1 → Callback is registered
• value (integer)
  • Sensor data value
  • Can be positive, negative, or zero

Both values are space-separated and provided on a single line.

Output Format:

• If flag is 0, print:

  • NO CALLBACK 

• If flag is 1, invoke the callback and print:

  • DATA <value>
    

The output must match exactly, with no extra spaces or text.

Example 1

Input:

0 10

Output:

NO CALLBACK 

Example 2

Input:

1 25

Output:

DATA 25 

Constraints:

• Use nullptr to represent the absence of a callback
• Always check the callback pointer before calling it
• value fits within a 32-bit signed integer
• Do not invoke a null function pointer