Duration of 1 second during while(ros::ok())

edit

You essentially have the code, you just need to modify your rate value. Right now you have 50 which will run at 50Hz (i.e. 50 times per second), so you should set that value to 1 so that it runs only once per second. Your code would be:

 int main()
 {
     //Declaration part
     ros::Rate rate(1); // periodic at 1 cycle per second
     while(ros::ok())
     {
         // Run your function and check condition

         // Modify the message based on the condition

         // Publish the message

         rate.sleep(); // runs out whatever duration is remaining for the 1 second interval
         ros::spinOnce();
     }
 }

Using the Rate will try to maintain your loop running at the period you specify. For example, if your function call took 0.5 seconds, the Rate will fill in the remaining 0.5 seconds, and your loop will take 1.0 seconds in total. This page gives a nice overview of your options.