Nested control structures refer to placing one control structure (like if, for, while, or switch) inside another. This allows programmers to handle more complex decision-making and repetitive tasks in a structured way. For example, an ‘if’ statement inside a ‘for’ loop can be used to check a condition on each iteration. Similarly, a ‘while’ loop can be placed within another ‘while’ loop to process multi-level logic, such as matrix operations or menu-driven programs.

Proper indentation is very important when using nested structures. It helps in understanding which block of code belongs to which control structure. Without proper indentation, the code becomes confusing and harder to debug. Even if the code works, poor formatting can make future updates or troubleshooting more difficult.

While nesting is powerful, too many levels of nesting can reduce code readability and make it harder to understand. If you find yourself nesting three or more levels deep, it may be a good idea to break the logic into smaller, reusable functions. This not only simplifies the main program but also promotes code reuse.

Using functions to manage complex nested blocks makes your code more modular and easier to test. When testing nested structures, ensure all possible conditions and edge cases are checked to avoid logical errors. Also, be careful with braces {} to clearly define the beginning and end of each block.