Input Validation and Error Handling

[MakaremHind]

Description:

This pull request adds important input validation checks to improve the robustness and user experience of the calculator application. The following enhancements were implemented:

• Prevent Multiple Decimal Points:

  Prevents users from entering multiple decimal points within a single number, which could lead to invalid inputs or parsing errors.

• Prevent Consecutive Operators:

  Prevents users from adding two operators consecutively.

• Division by Zero Check:

  Adds validation to handle division by zero, displaying an error message when a user attempts to divide by zero.

The code is now more resilient to unexpected user inputs, providing a smoother and more reliable user experience.