Possible cross-platform compatibility issue

**Describe the bug**
The build might fail due to a missing dependency on Windows-based systems

**To Reproduce**
Compile on Windows

**Expected behavior**
Compilation should be successful.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Desktop (please complete the following information):**
- OS: Ubuntu 20.04

**Additional context**
Possibly due to missing `regex.h` library present on POSIX-Compliant systems.

Start by compiling the phonebook project on Windows and confirming whether the failure is caused by the POSIX-only regex.h dependency. Search the codebase for regex.h usage and any platform-specific build instructions. Done means the project compiles successfully on Windows without breaking POSIX builds.

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