How to solve problems related to Number-Digits using Recursion?

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:

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.
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:

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

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My Personal Notes

C++

Java

Python3

C#

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