# Recursive Function :

A recursive function is a function that calls itself during its execution, either directly or indirectly. It is a powerful and elegant technique that allows solving complex problems by breaking them down into smaller and simpler subproblems, and then combining the results to obtain the final solution.

This article covers a lot of practice questions on recursion, which is a common topic in programming interviews and exams. By going through these questions, you can gain a deeper understanding of how recursion works and how to apply it to solve a variety of problems.

# Let’s start to understands What is Recursive Function?

A recursion function is a function that calls itself repeatedly until a base case is reached. Recursion is a powerful technique in programming that allows a problem to be broken down into smaller, simpler sub-problems. Each sub-problem is solved using the same algorithm as the original problem, but with a smaller input size. The base case represents the simplest possible input for the function, and it allows the recursion to terminate.

The key to writing a good recursive function is to ensure that it eventually reaches the base case, and that the result obtained from each recursive call is combined in a meaningful way to produce the final result. Recursion can be used to solve a wide range of problems, including complex mathematical calculations, data structures like trees and graphs, and other algorithms.

One of the advantages of recursion is that it can make code more concise and easier to understand, as it avoids the need for explicit loops and repetitive statements. However, recursion also has some potential drawbacks, such as increased memory usage and the risk of stack overflow if the function calls itself too many times. Therefore, it is important to use recursion judiciously and with care.

# Working Flow of Recursion Function :

The working flow of a recursive function can be explained using the following steps:

- The recursive function is called with some input parameters.
- The function checks if the base case has been reached. If the base case is satisfied, the function returns a value, otherwise, it proceeds to step 3.
- The function calls itself with a modified set of input parameters. This is known as the recursive case, and it leads to the function being called repeatedly until the base case is reached.
- Each time the function calls itself, a new instance of the function is created with its own set of local variables and input parameters.
- The function continues to call itself recursively until the base case is reached.
- Once the base case is reached, the final value is returned and the recursive calls begin to unwind.
- As each instance of the function completes, its local variables and input parameters are removed from the stack, and control is returned to the previous instance of the function.
- The process continues until the original function call completes, and the final result is returned.

It is important to note that recursive functions require a base case to prevent infinite recursion, which can cause stack overflow errors and crash the program. A well-written recursive function should be designed to reach the base case in a finite number of steps.

# Advantages of Recursion Function :

Recursion is a powerful technique in programming that has several advantages:

**Clarity and Readability:**Recursion can make code more readable and easier to understand, especially when dealing with problems that can be naturally broken down into smaller, self-similar sub-problems.**Reducing Code Length:**Recursion can reduce the length of code required to solve a problem, as it avoids explicit loops and repetitive statements.**Simplicity:**Recursive code can be simpler and more concise than iterative code, as it avoids the need for a counter variable, loop control structures, and other associated syntax.**Flexibility:**Recursion can be used to solve a wide range of problems, including complex mathematical calculations, data structures like trees and graphs, and other algorithms.**Efficiency:**In some cases, recursive functions can be more efficient than their iterative counterparts, as they can save memory and processing power by breaking down the problem into smaller sub-problems.

# Drawbacks of Recursion Function :

While recursion has several advantages, it also has some potential drawbacks that programmers need to keep in mind:

**Stack Overflow:**Recursion can lead to a stack overflow error if the recursive function calls itself too many times. This happens when the system stack runs out of memory due to too many recursive function calls, causing the program to crash.**Memory Usage:**Recursive functions can use up a lot of memory, as each function call requires a new stack frame to be created. If the recursion is deep, the number of stack frames can quickly add up, leading to high memory usage.**Performance:**Recursive functions can be slower than iterative functions in some cases, as each function call requires extra overhead to create and manage a new stack frame.**Difficulty of Debugging:**Recursive functions can be difficult to debug, as they often involve multiple levels of nested function calls that can be hard to trace.**Difficulty of Understanding:**While recursion can make code simpler and more concise in some cases, it can also make the code harder to understand, especially for novice programmers who may not be familiar with the concept.

Let’s Practice some questions on recursion :

Question : Write a program to print the first 50 natural numbers using recursion. |

Solution : Click here to view answer. |

Question : Write a program to calculate the sum of numbers from 1 to n using recursion. |

Solution : Click here to view answer. |

Question : Write a program to count the digits of a given number using recursion. |

Solution : Click here to view answer. |

Question : Write a program to find the sum of digits of a number using recursion. |

Solution : Click here to view answer. |

Question : Write a program to calculate reverse of a number. |

Solution : Click here to view answer. |

Question : Write a program to find Factorial of a number. |

Solution : Click here to view answer. |

Question : Write a program to find the GCD of two numbers using recursion. |

Solution : Click here to view answer. |

Question : Write a program to convert a decimal number to binary using recursion. |

Solution : Click here to view answer. |

Question : Write a program to print even or odd numbers in a given range using recursion. |

Solution : Click here to view answer. |

Question : Write a program to calculate the power of any number using recursion. |

Solution : Click here to view answer. |

Question : Write a program to Find Product of Two Numbers using Recursion |

Solution : Click here to view answer. |

Question : Write a program to print the Fibonacci Series using recursion. |

Solution : Click here to view answer. |

Question : Write a program to print all even digit from a number using recursion. |

Solution : Click here to view answer. |

In conclusion, recursive functions are a powerful and elegant tool in programming that can help solve complex problems by breaking them down into smaller and simpler subproblems. By understanding the principles of recursion and practicing with a variety of questions, you can become more proficient in using recursion and develop a deeper understanding of how it works.

This article has covered a lot of practice questions on recursion, which can help you improve your recursion skills and prepare for programming interviews and exams. By working through these questions and understanding the explanations and solutions provided, you can gain confidence in your ability to use recursion to solve a variety of problems.

Remember that recursion is just one tool in your programming toolbox, and it may not always be the most efficient or appropriate solution for every problem. It’s important to choose the right tool for the job and understand the trade-offs between different approaches.

By mastering recursion and other programming techniques, you can become a more versatile and effective programmer, capable of solving a wide range of problems and delivering high-quality code. Keep practicing and learning, and you’ll be on your way to becoming a recursion expert in no time!