The core challenge of this project was managing the calculator's state—specifically, distinguishing between entering a new number and operating on a previous result. To solve this, I designed a state machine based on a "Two Worlds" concept.
"Only the first action after
=matters."
The state of the calculator is defined entirely by what the user does immediately after a calculation is completed.
This is the default state. The calculator accepts input into a buffer ("Editing Mode").
- Input: User types numbers into the edit buffer.
- Locking: Clicking an operator "finalizes" the first number and moves the calculator into a waiting state for the second operand.
- Calculation: Clicking
=finalizes the second number, computes the result, and transitions the system to World 2.
Once a result is displayed, the calculator waits for the "First Action" to determine the path forward:
- Path A: Continue Calculation (User clicks an Operator)
- The current result is treated as the new first operand.
- The system immediately locks this number and waits for a new second operand.
- Path B: Restart (User clicks a Number)
- The system interprets this as a desire to start fresh.
- The result is discarded, the screen clears, and the user is returned to World 1.
The logic constantly switches between:
- Editing Mode: The user is actively constructing a number (typing digits).
- Finalizing Mode: A number has been locked in by an operator or equal sign.
Special Exceptions:
The keys DEL, %, +/-, and . act as "bridge" keys. If pressed while in World 2 (displaying a result), they force the system back into Editing Mode, allowing the user to modify the previous result before using it in a new calculation.
- Standard Operations: Add, Subtract, Multiply, Divide.
- Sign Toggling: Swap between positive and negative values (
+/-). - Percentage: Converts current value to a percentage.
- Backspacing:
DELbutton to remove the last digit entered. - Precision Handling: Outputs are formatted to avoid floating-point overflow on the display.s