You are going to have to be rather more clever than that - that's just your "value operator value equals" code which doesn't really cut it when you start working with multiple operators.
And ... what if I type "2 * 3 + 4" and "4 + 2 * 3"?
Operator precedence rules say I should get the same result for both: 10.
But unless you add that to your code you will get 10 and 18!
What I'd suggest is that - if you must go down the "button for each possible input" route - you need to be a lot more "clever" about what you are doing and eitehr convret the user input into Reverse Polish notation
] and stack it internally, or store your operators as "tokens" as they are entered and process them "properly" once Equals is pressed.
Me? I'd throw the lot away and do something a bit more Windows "user freindly" like Microsoft Mathematics
] (Though the latest version has ... um ... bloated somewhat from teh svelte original!)
You can get it free from MS: Download Microsoft Mathematics 4.0 from Official Microsoft Download Center