Hi Alece, thank you for your help. If the user inputs r < 0, then I wanted to cout something like this : cout << You should have entered a positive value of radius. For ex:
If ( r > 0 )
}
If command is diameter, do diameter = 2 * r
else if command is perimeter do this...
else if command is area do this....
}
else if ( r < 0 )
}
cout << "You should have enter a positive value for radius." << endl;
}

return o;