OldPhonePad Converter

This project implements an OldPhonePad converter in C#, which simulates the text input method used on old mobile phone keypads. It converts a sequence of number key presses into the corresponding text.

Features

• Converts number sequences to their corresponding letters based on old phone keypad layout
• Handles repeated key presses to cycle through available letters
• Supports backspace functionality using the * character
• Ignores spaces in the input
• Requires # at the end of each input to signify completion

How It Works

The converter uses the following keypad mapping:

• 1: &'(
• 2: ABC
• 3: DEF
• 4: GHI
• 5: JKL
• 6: MNO
• 7: PQRS
• 8: TUV
• 9: WXYZ
• 0: (space)

Repeated presses of the same key cycle through the available letters. For example, pressing '2' once gives 'A', twice gives 'B', and three times gives 'C'.

Usage

To use the OldPhonePad converter, call the ConvertToOldPhonePad method of the OldPhonePad class:

string result = OldPhonePad.ConvertToOldPhonePad("228#");
Console.WriteLine(result); // Output: BAT

Make sure to end each input with '#' to signify the end of the input sequence.

Examples

1. Basic conversion:

   OldPhonePad.ConvertToOldPhonePad("33#") // Returns: E

2. Using backspace:

   OldPhonePad.ConvertToOldPhonePad("227*#") // Returns: B

3. Spelling a word:

   OldPhonePad.ConvertToOldPhonePad("4433555 555666#") // Returns: HELLO

4. Complex input:

   OldPhonePad.ConvertToOldPhonePad("8 88777444666*664#") // Returns: TURING

Error Handling

The converter will throw an ArgumentException in the following cases:

• If the input is empty
• If the input doesn't end with '#'
• If the input contains invalid characters (anything not in the keypad mapping or special characters)

Contributing

Feel free to fork this project and submit pull requests with improvements or bug fixes. If you find any issues, please open an issue in the project repository.

License

This project is open source and available under the MIT License.