Except (0,0), if I enter any point on coordinate axes I am not getting the correct answer. For example If I enter (1,-0.01) I should get an angle close to 2*pi. On (1,0), I should get pi/2. For (-1,0), (0,-1) I should get pi and 3*pi/2 respectively. Do I need to redefine atan function on the coordinate axes? Please help.

real x,y,s;

cout<<"Enter x-coordinate : ";

cin>>x;

cout<<"Enter y-coordinate : ";

cin>>y;

s=atan(y/x);

cout<<"Polar angle of the coordinate is : ";

cout<<s;