High-Level Design (HLD) and Low-Level Design (LLD) are software design concepts that are not specific to any programming language. However, to illustrate the differences between HLD and LLD, we can use C# programming language examples. Suppose we are designing a software system that involves creating a payment gateway application in C#. Here are examples of HLD and LLD for this system: High-Level Design (HLD): Define the functional requirements of the payment gateway system, such as processing payment transactions, handling errors, and providing a user interface. Identify the non-functional requirements, such as performance, scalability, and security. Identify the key components of the payment gateway system, such as payment processing engine, database, user interface, and error handling. Create an architecture diagram that shows how these components will fit together to form the payment gateway system. In HLD, the focus is on defining the system's overall structure and architectu