C++ is a low-level language suitable for system-level applications with manual memory management, while C# is a high-level language designed for simplicity and modern applications with automatic garbage collection. Key differences include their performance, complexity, and use cases; C++ is better for high-performance needs, while C# excels in web and enterprise applications. Both share a similar syntax and support object-oriented programming, but each has distinct libraries and frameworks tailored to their ecosystems.