Code doesn't work inside a loop but works outside the loop

Question

I have a piece of code which is showing some weird behaviour. The code works as expecred when it is kept out of the for loop but once I place it inside the for loop, it just keeps on repeating the same value once and again.

  const double *north = cp->getValues();
  angle1 = atan2(north[1], north[2]);
  bearing = (angle1 - 1.5708) / M_PI * 180.0;
  std::cout<<"Bearing inside : "<<bearing<<std::endl;
  if (bearing < 0.0)
    bearing = bearing + 360.0;
  t = abs(bearing - turn);

This portion of code to supposed to update the *north everytime the object rotates. This happens whenever I keep this code outside my loop. But once the code is kept inside a for loop as shown below, the value of *north remains constant.

    for(int i=0;i<100;i++)
    {
      double t_modifier = (180.0 - abs(t)) / 180.0;
      double threshold = 2.0;
      double Speedleft = 1.0;
      double Speedright = 1.0;
      int identifier;
      if(int(t)<0){
        Speedleft = -1;
      }
      else if(int(t)>0){
        Speedright = -1;
      }
      leftSpeed = threshold * Speedleft;
      rightSpeed = threshold * Speedright;
      {
        wheels[0]->setVelocity(leftSpeed);
        wheels[1]->setVelocity(rightSpeed);
        wheels[2]->setVelocity(leftSpeed);
        wheels[3]->setVelocity(rightSpeed);
      }
      
      const double *north = cp->getValues();
      angle1 = atan2(north[1], north[2]);
      bearing = (angle1 - 1.5708) / M_PI * 180.0;
      std::cout<<"Bearing inside : "<<bearing<<std::endl;
      if (bearing < 0.0)
        bearing = bearing + 360.0;
      t = abs(bearing - turn);
    }

Answer 1

You should call the step method in the loop:
https://cyberbotics.com/doc/reference/robot#wb_robot_step

An in-depth explanation of the step method:
https://cyberbotics.com/doc/guide/controller-programming#the-step-and-wb_robot_step-functions