Shoot Script Conversion error

Good night.

I´m newby in unity, I have some knowledge in C# programmer, but I couldn’t convert this script in JS, to C#, please can someone help me to correct it:

JS Script
#pragma strict
var velTiro = 550.0;
var balaObj : GameObject;
function Start () {

}

function Atira(){
	var bala = Instantiate(balaObj, transform.position, transform.rotation);
	bala.tag = "bala";
	
	bala.AddComponent(Rigidbody);
	bala.transform.position = transform.position;
	bala.transform.rotation = transform.rotation;
	
	bala.rigidbody.velocity = transform.forward * velTiro * -1;
	bala.transform.TransformDirection( Vector3(0,0,velTiro));
	bala.rigidbody.mass = 1;
	audio.Play();
}

function Update () {
	if (Input.GetButtonDown("Fire1")){
		Atira();
	}
}

My C# code looks like:

using UnityEngine;
using System.Collections;

public class arma : MonoBehaviour {
	float velTiro = 550f;
	public GameObject balaObj;
	
	// Use this for initialization
	void Start () {
	
	}
	
	void Atira(){
		Rigidbody bala;
		bala = Instantiate( balaObj, transform.position, transform.rotation) as Rigidbody;
		bala.tag = "bala";
		bala.position = transform.position;
		bala.rotation = transform.rotation;
		bala.velocity = transform.forward * velTiro * -1;
		bala.mass = 1;
		
		// Para adicionar som de tiro
		//audio.Play();
	}
	
	// Update is called once per frame
	void Update () {
		// Atira quando aperta tela esquerda do mouse, Fire1
		if ( Input.GetButtonDown("Fire1")){
			Atira();
		}
	}
}

It throws a NullPointerException just after try to instantiate the Rigidbody bala.

Thanks for the help!

Are you initializing ‘balaObj’ in the inspector? If you don’t, you will get a null reference exception. Here is a bit more literal conversion with a few other cosmetic changes:

using UnityEngine;
using System.Collections;

public class arma : MonoBehaviour {
    float velTiro = 550.0f;
    public GameObject balaObj;

    void Atira(){
       GameObject bala = Instantiate(balaObj, transform.position, transform.rotation) as GameObject;
       bala.tag = "bala";
       bala.transform.position = transform.position;
       bala.transform.rotation = transform.rotation;
       bala.rigidbody.velocity = transform.forward * velTiro * -1.0f;
       bala.rigidbody.mass = 1.0f; 

       // Para adicionar som de tiro
       //audio.Play();
    }

    void Update () {
       // Atira quando aperta tela esquerda do mouse, Fire1
       if ( Input.GetButtonDown("Fire1")){
         Atira();
       }
    }
}