**Cosmic Physics Calculator v1.0** is an advanced, terminal-based computational suite engineered in pure ANSI C for astrophysicists, cosmologists, and physics students. Designed for cross-platform use on Windows, Linux, and macOS, it delivers 40 specialized modules spanning classical mechanics, thermodynamics, quantum physics, special/general relativity, and cosmology. Core capabilities include Schwarzschild radius calculation, Hubble parameter evolution at arbitrary redshift, Jeans mass estimation, Eddington luminosity, relativistic Doppler effects, and plasma physics metrics (Debye length, plasma frequency). Built with a comprehensive database of standardized physical constants (G, c, h, kB, H₀, M⊙) and strict double-precision arithmetic, the tool ensures scientific accuracy for academic and preliminary research workflows. Its modular procedural architecture encapsulates each physics domain in dedicated functions, called via a central menu dispatcher, while robust input validation (`get_double_input()`) prevents mathematical errors and handles non-numeric entries gracefully. Results are formatted in scientific notation (`%.2e`) for extreme values or fixed-point for standard magnitudes, with contextual unit prompts reducing conversion mistakes. The thermodynamics module uniquely validates Ideal Gas Law consistency (PV≈nRT), and the cosmology engine implements a simplified ΛCDM model for H(z) calculations. Requiring only `` and standard C libraries, the application compiles to a compact, zero-dependency binary via `gcc -lm`. With MIT licensing, transparent source code, and portable compilation flags, Cosmic Physics Calculator invites customization, extension, or pedagogical exploration—transforming complex astrophysical formalisms into accessible, offline-capable computations for researchers and educators alike. 🔭🌌🧮