# Indirect Recursion in C

## What is indirect recursion?

Indirect recursion in C is a type of recursion where a function calls another function, which in turn calls the original function or another function that eventually calls back the original function.

In indirect recursion, there is a cycle of function calls that continues until some condition is met to stop the recursion. This cycle can involve any number of functions, each calling the next function in the cycle, creating a loop of function calls.

Indirect recursion can be a powerful tool for solving certain types of problems, but it can also lead to stack overflow errors if the recursion is not properly managed. It is important to keep track of the function calls and ensure that the recursion terminates at some point to avoid infinite looping.

## Why we use indirect recursion in C?

Indirect recursion can be useful in solving certain types of problems where a cyclic pattern exists. It allows a group of functions to call each other in a loop, with each function calling another function that eventually calls back to the original function.

One of the main advantages of indirect recursion is that it can simplify the logic of the code, by breaking down a complex problem into smaller sub-problems that can be solved recursively.

For example, in graph traversal algorithms, such as depth-first search or breadth-first search, a recursive function can be used to explore the neighbouring vertices of a graph, and the call to the function can be passed from one vertex to another in a cyclic pattern.

Indirect recursion can also be used in algorithms that involve backtracking, where the algorithm needs to undo previous steps and try a different path to find a solution. In this case, the recursive calls can be used to backtrack to the previous state of the algorithm and explore other paths.

However, it is important to note that indirect recursion can be more difficult to understand and debug than simple recursion. It is also more prone to infinite looping and stack overflow errors if the recursion is not properly managed, so it should be used with caution.

## Characteristics of Indirect Recursion

The characteristics of indirect recursion in programming are as follows:

1. In indirect recursion, a group of functions call each other in a cyclic pattern, with each function calling another function that eventually calls back to the original function.
2. It is a form of recursion where the function calls itself indirectly through another function, instead of calling itself directly.
3. Indirect recursion can be used to solve problems that have a cyclic pattern, such as graph traversal algorithms and backtracking algorithms.
4. It can simplify the logic of the code by breaking down a complex problem into smaller sub-problems that can be solved recursively.
5. The order of the function definitions does not matter, as long as they are declared before they are called.
6. Indirect recursion can lead to infinite loops if not properly managed, so it is important to keep track of the function calls and ensure that the recursion terminates at some point.
7. It can be more difficult to understand and debug than simple recursion, especially if the cycle of function calls is complex and involves many functions.

## How does indirect recursion work?

The working of indirect recursion in programming involves a cycle of function calls that continues until some condition is met to stop the recursion. In indirect recursion, a group of functions call each other in a cyclic pattern, with each function calling another function that eventually calls back to the original function or another function in the cycle.

Here is an example of how indirect recursion works in C:

Example:

``````#include <stdio.h>
void foo(int n);
void bar(int n) {
if (n > 0) {
printf("%d ", n);
foo(n - 1);
}
}

void foo(int n) {
if (n > 0) {
printf("%d ", n);
bar(n - 1);
}
}
int main() {
foo(5);
return 0;
}``````

Output:

`5 4 3 2 1`

In this example, foo() calls bar(), which then calls foo() again, creating a cycle of function calls that continues until the input parameter reaches 0.

When the program executes, foo() is called with a parameter of 5. The foo() then checks if the parameter is greater than 0, which it is, so it prints 5 and calls bar() with a parameter of 4. The bar() checks if its parameter is greater than 0, which it is, so it prints 4 and calls foo() with a parameter of 3. This cycle of function calls continues until the parameter reaches 0, at which point the recursion stops.

The order of the function definitions does not matter in indirect recursion, as long as they are declared before they are called. This is because the compiler only needs to know that the functions exist before they are called, and it will resolve the references to the functions at link-time.

It is important to keep track of the function calls in indirect recursion and ensure that the recursion terminates at some point, to avoid infinite looping and stack overflow errors. Properly managing the recursion can help avoid errors and ensure that the code behaves as expected.