What is recursive calls.which data structure is used in it?

Answer 1

A recursive call is any function that calls itself with modified parameters. There is no data structure associated with it, other than the call stack which is associated with all function calls, recursive or not. The stack is used to store the state of the current instance's local variables, the return address, and the arguments to be passed to the next instance. This allows recursive calls to "unwind" in the reverse order they were called.

Recursive functions must have a terminating condition as all the recursive calls must eventually return to the original caller at some point. If they don't, they'll simply keep calling themselves until there's no more space on the stack.

Recursive functions are commonly used in divide-and-conquer algorithms, gradually reducing larger problems down to smaller instances of the same problem until a terminating condition is satisfied. As the calls return, the larger problem is gradually solved until the function returns to the original caller, at which point the entire problem is fully resolved. Quicksort is a typical algorithm that makes use of recursion.