In the software, the required keystrokes can be defined per key. For instance:

  press = 1; // Function
  set("int () { // ~"); 
  set("   ;~"); 
  set("  return 0; ~"); 
  set("}; // func~^^^<<<<<<<<"); 

 Will result in the following code:

int () { // 
   ;
  return 0; 
}; // func

And the cursor is placed between the brackets (). The following special characters are used:

< left arrow, 

^ top arrow, 

> right arrow, 

# delete, 

~ enter 

Please keep in mind:

•  Use the Adrduino Leonardo for programming, not the Pro!      
•  Unplug the Arduino pro and replug when compiling has started 
•  Or attach a reset button and press the reset button while compiling and release this button when "Waiting for upload port..." is shown.           
•  Connect pin A3 to ground, to cancel all keyboard presses (emergency stop).    
•  Macro Pad is ready for use when blue light is off.      

Libraries used:

The input: https://playground.arduino.cc/Code/Keypad/ 

The output: https://docs.arduino.cc/language-reference/en/functions/usb/Keyboard/