Calculator Project

Overview

This project is a simple calculator that evaluates expressions step by step as the user inputs values, rather than following traditional BODMAS rules. Instead of waiting for a complete mathematical expression, the calculator immediately updates the result after each operator is pressed.

Core Functionality

The project relies on three main variables to store user inputs and five important flags to track user interactions and calculation states.

Visual Demo

### When making impossible calculations

Variables:

• liveVar: Holds the current active number or result of calculations.
• secVar: Temporarily stores the second number in an operation.
• oprVar: Stores the selected operator (+, -, *, /, etc.).

Flags (Boolean values used to track program states):

• isOprClicked: Tracks whether an operator has been pressed. This is crucial because when isOprClicked is true, any new number input should be stored in secVar instead of liveVar. It also ensures calculations happen only when an operator is followed by a second number.
• checkerForLive: Ensures numbers are displayed correctly when entered. When checkerForLive is true, the next number input completely replaces the current value on the display instead of appending to it. This prevents unwanted number concatenation and ensures a clean UI experience. It is reset to false after the number is entered.
• checkerForEqualsInPer: Ensures that percentage operations apply correctly. Without this, percentages might be calculated incorrectly when used after the equals button.
• checkerForFlag: Prevents unintended duplicate calculations when switching operators after pressing =. Without it, switching operators could cause the last operation to repeat unintentionally.
• checkerForDelete: Determines whether a delete action should remove digits from liveVar or secVar, preventing unwanted changes to stored values.

Calculation Scenarios

Scenario 1: Basic Calculation (Ideal Flow)

Example: 2 + 4 =

1. User inputs 2, which is stored in liveVar.
2. User presses +. This:
   • Stores + in oprVar.
   • Sets isOprClicked to true, indicating that the next number should be stored in secVar.
   • Sets checkerForLive to true, ensuring that the next number input replaces the existing value on the display.
3. User inputs 4, which is now stored in secVar (since isOprClicked is true).
4. User presses =. This triggers the calculation:
   • 2 + 4 = 6
   • The result (6) is stored in liveVar.
   • secVar is cleared for future calculations.
   • checkerForLive is set to true, so if the user enters a new number, it replaces 6 instead of appending to it.
5. The calculator is now ready for the next input.

Scenario 2: Continuous Calculation (Chained Operations)

Example: 12 * 4 - 81

1. User inputs 12, stored in liveVar.
2. User presses *, which:
   • Stores * in oprVar.
   • Sets isOprClicked to true.
   • Sets checkerForLive to true to ensure the next number replaces the current display.
3. User inputs 4, stored in secVar.
4. User presses -, triggering the multiplication:
   • 12 * 4 = 48
   • The result (48) is stored in liveVar.
   • secVar is cleared.
   • oprVar is updated to -, preparing for the next operation.
   • checkerForLive is set to true.
5. User inputs 81, which is stored in secVar.
6. Further calculations follow the same pattern.

Special Cases and Edge Handling

Handling Operator Switching (checkerForFlag)

When a user presses =, then changes the operator, checkerForFlag prevents unnecessary recalculations. Example: 2 + 5 = - 4

• Without checkerForFlag, 4 might be subtracted twice, leading to incorrect results.

Ensuring Correct Percentage Calculations (checkerForEqualsInPer)

If the user presses % after an operation, it ensures the percentage is calculated relative to the total. Example: 5 + 5 %

• Instead of treating 5% as 0.05, the program correctly calculates 10% of 10, resulting in 1.0.

Managing Deletion (checkerForDelete)

If the user deletes a number, the program needs to know whether to modify liveVar or secVar.

• If isOprClicked is true, deletion should affect secVar.
• If isOprClicked is false, deletion modifies liveVar.

Conclusion

This project showcases an interactive approach to real-time calculations by prioritizing user input flow. The flag system ensures calculations behave predictably, providing a seamless experience for users. Through careful state management, the calculator allows for continuous operations, correct handling of percentages, and intuitive input correction.