STATUS 3/operand1: value1operand2: nullopertor: +||-||*||/result: nullscreenNum: +=btn
STATUS 4/operand1: value1operand2: screenNumopertor: +||-||*||/result: calculate()screenNum: +=result
press =
press 0~9
press +-*/
press +-*/STATUS MACHINE FINISHED
press 1~9
press 0+-*/=STATUS MACHINE NULL
STATUS 2/operand1: screenNumoperand2: nullopertor: +||-||*||/result: nullscreenNum: value
INIT STATUS/operand1: nulloperand2: nullopertor: ''result: nullscreenNum: 0
STATUS 1/operand1: nulloperand2: nullopertor: ''result: nullscreenNum: += btn
