C# Recursive Functions Guide

A recursive function is a function that calls itself within its own body. It is a common programming technique used to solve cases that can be broken down into smaller instances of the same problem. In C#, the usage of recursive functions is as follows:

1. Identify the termination condition for the recursive function: A recursive function must have one or more termination conditions to avoid infinite loops.
2. The logic of executing a recursive function is defined as follows: the recursive function should call itself according to certain rules, and each call should have parameters that result in a smaller size of the current problem.
3. Handling the return value of a recursive function: A recursive function can have a return value, which can be obtained by combining its own return value with the solution to the current problem to achieve the final result.

Below is a classic example used to calculate factorials:

public static int Factorial(int n)
{
    // 终止条件
    if (n == 0)
    {
        return 1;
    }
    // 递归调用
    return n * Factorial(n - 1);
}

In the example above, the recursive function Factorial calculates the factorial of a given integer n. When n is equal to 0, the recursive function returns 1 as the termination condition. Otherwise, the recursive function calls itself with n-1 as the parameter and multiplies the return value by n to get the final result.

One advantage of using recursive functions is that they can break down complex problems into smaller sub-problems and solve them by calling themselves multiple times. Recursive functions are usually more concise in implementation than iterations, but they may sometimes suffer from performance losses.

It is important to note that when using a recursive function, you must ensure that the recursion depth is not too deep, otherwise it may result in a stack overflow issue.