thatsnotme:
how to convert gcode into Arduino C language?
That is not what you do.
You need to interpret the GCode to obtain the numbers of steps, and step-speeds for the motors.
is that lib will make cnc work even i dont have grbl?
I think you have your terminology confused. GRBL is a complex program for the Arduino that interprets GCode to produce instructions for stepper motors. I presume what you refer to as a "GRBL shield" is a piece of hardware intended for use with the GRBL software. I also presume that it is possible to use the GRBL software without using the GRBL shield as long as you correctly relate the pins controlling the stepper motors to the software. I have not used GRBL so I don't know how that is done - but I presume there are instructions somewhere.
I had assumed when you asked about not using the GRBL shield that you were also excluding the use of the GRBL software.
For my small lathe I decipher the GCode on my PC and just send simple motor movement data to the Arduino.
...R