For loop contaning a subscriber does just the first iteration

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I did what you said but still i never changes( always 1) .I put the pub and sub before the for loop but it didn't work and for nbr defined in the pid_node class it is always 0 even that i is 1 it supposed to take the value of i .i did it just to see if it is there any iteration.

10 * i does not mean i * =10. And your problem was that there was only one iteration of the for loop. How many iterations does it do now? I didn't try to debug your code, I just tried to explain how spin and spinonce works.

i changed it i did i++ and still not working. what i m asking is that if we call a callback function that is defined as a methode in a class how to get back to the main code and change the arguments for the class

callback functions are called every time their node spins and there are new data available. If you want to use the received data you can write your algorithm in the callback function, otherwise you should asign the received value to a class member variable and use that variable in a another class ..

function. Make sure that you use new data on every run. This means that your function or main code should be called after a spin of the node. i.e. main(){ ...

while(ros::ok()){ do_something(); spinOnce(); ros::Duration(1.0).sleep(); } }