Guide to implement code with Gazebo

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BH

I would like to implement a code that moves a turtlebot straightforward and see it on Gazebo. At first, I tried to paste the code i a Gazebo Plugin but it looks like when I run a launch file that sets the robot on a planned world, it doesn't respond.

This is the code(without implementation in a Gazebo plugin):

/*
 * * Hello World and Crash for Turtlebot
 * * Moves Turtlebot forward until you ctrl + c
 * * Tested using TurtleBot 2, ROS Indigo, Ubuntu 14.04
 * */

#include <iostream>
#include <ros ros.h="">
#include <geometry_msgs twist.h="">

int main(int argc, char** argv)
{
    //init the ROS node
    //    ROS_INFO_STREAM("Hello World");
    //        ros::init(argc, argv, "robot_driver");
    //            ros::NodeHandle nh;
    //
    //                //init publisher
    //                    ros::Publisher cmd_vel_pub_;
    //                        cmd_vel_pub_ = nh.advertise<geometry_msgs::twist>("cmd_vel_mux/input/teleop", 1);
    //                            
    //                                //init direction that turtlebot should go
    //                                    geometry_msgs::Twist base_cmd;
    //                                        base_cmd.linear.x = base_cmd.linear.y = base_cmd.angular.z = 0;
    //
    //                                            //and let's go forward by setting X to a positive value
    //                                                base_cmd.linear.x = 0.25;
    //
    //                                                    ROS_INFO_STREAM("And Crashing ... ctrl + c to stop me :)");
    //
    //                                                        while(nh.ok()) { //have we ctrl + C?  If no... keep going!
    //                                                                //"publish" sends the command to turtlebot to keep going
    //                                                                      cmd_vel_pub_.publish(base_cmd);
    //                                                                          }
    //                                                                          }

</code<>

What should I do?
 
P.S
By the way, how come I can't see the cmd_vel_mux topic by picking the topic visualization tab on Gazebo?