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How to solve problems related to Number-Digits using Recursion?
  • Last Updated : 22 May, 2020

The process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called a recursive function. Using a recursive algorithm, certain problems can be solved quite easily. A method to solve the number digit problems using recursion is discussed in this article.

Two main components exist for any recursive function are:

  1. Base Case: A base case is a condition which stops the recursive function calls. A recursive function cannot be formed without a base case because the stack overflow error occurs when the base case is not defined as the function will keep on repeatedly calling itself. For a recursive solution, there can be more than one base case.
  2. Recursive Case: For all the other conditions apart from the base cases, the function calls itself with a new set of values such that after some finite recursive calls, the function finally calls for a base case and stops itself.

Let’s visualize the recursion by extracting individual digits from a given number. This is the basic step in performing many other mathematical operations.

Below is the implementation to extract every individual digit of a number:

C++




// Recursive function to extract
// individual digit for a given
// number
#include<bits/stdc++.h>
using namespace std;
  
void extract(int n){
  
    // If n is a single digit
    // number, then print the
    // digit and break stop 
    // the recursion
    if(n / 10 == 0)
    {
        cout << n;
        return;
    }
  
    // If n is not a single
    // digit number, then 
    // print the last digit
    cout << n % 10 << endl;
  
    // Call the function recursively
    // for n // 10 which basically
    // calls for the remaining number
    // after removing the last digit
    return extract(n / 10);
}
  
// Driver code
int main()
{
    extract(1001);
    return 0;
}
  
// This code is contributed by 29AjayKumar

Java




// Recursive function to extract
// individual digit for a given 
// number
class GFG{
  
static void extract(int n)
{
      
    // If n is a single digit
    // number, then print the
    // digit and break stop 
    // the recursion
    if(n / 10 == 0)
    {
        System.out.print(n);
        return;
    }
  
    // If n is not a single
    // digit number, then 
    // print the last digit
    System.out.print(n % 10 + "\n");
  
    // Call the function recursively
    // for n // 10 which basically
    // calls for the remaining number
    // after removing the last digit
    extract(n / 10);
}
  
// Driver code
public static void main(String[] args)
{
    extract(1001);
}
}
  
// This code is contributed by Rohit_ranjan

Python3




# Recursive function to extract
# individual digit for a given
# number
def extract(n):
  
    # If n is a single digit
    # number, then print the
    # digit and break stop 
    # the recursion
    if(n//10 == 0):
        print(n)
        return
  
    # If n is not a single
    # digit number, then 
    # print the last digit
    print(n % 10)
  
    # Call the function recursively
    # for n // 10 which basically
    # calls for the remaining number
    # after removing the last digit
    return extract(n//10)
      
# Driver code
if __name__ == "__main__":
    extract(1001)

C#




// Recursive function to extract
// individual digit for a given 
// number
using System;
  
class GFG{
      
static void extract(int n)
{
      
    // If n is a single digit
    // number, then print the
    // digit and break stop 
    // the recursion
    if(n / 10 == 0)
    {
        Console.Write(n);
        return;
    }
  
    // If n is not a single
    // digit number, then 
    // print the last digit
    Console.Write(n % 10 + "\n");
  
    // Call the function recursively
    // for n // 10 which basically
    // calls for the remaining number
    // after removing the last digit
    extract(n / 10);
}
  
// Driver code
public static void Main(String[] args)
{
    extract(1001);
}
}
  
// This code is contributed by sapnasingh4991
Output:
1
0
0
1

Similar to this, various other operations can be performed using recursion. Every iterative function can be computed using the recursion.

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