Help with First Calculator Program

Hi, new to c# and visual studio. Just doing my first calc program. The add and subtract works ok but I cant get multiply and divide to work. I originally used booleans and so when add/subtract was clicked it would set the bools to true or false which worked ok.

But now I am trying to use a switch so i can understand it a bit. Please can someone look at my code and help me.

See attached