Recursive Program for Binary to Decimal

Last Updated : 30 Sep, 2022

Given a binary number as string, find its decimal equivalent.

Examples:

Input : binary = "101"
Output : 5

Input : binary = "1111"
Output : 15

We have discussed iterative solution to convert Binary to Decimal.
The idea is simple, we add current term and recur for remaining terms.

binary2decimal

C++

// Recursive CPP program to convert binary 
// decimal
#include<bits/stdc++.h>
using namespace std;

int toDecimal(string binary, int i=0)
{
    // If we reached last character
    int n = binary.length();
    if (i == n-1)
      return binary[i] - '0';
    
    // Add current tern and recur for
    // remaining terms
    return ((binary[i] - '0') << (n-i-1))  +
            toDecimal(binary, i+1);
}

// Driver code
int main()
{
    string binary = "1010";
    cout << toDecimal(binary) << endl;
    return 0;
}

Java

// Recursive Java program to convert binary 
// decimal


class GFG
{
    static int toDecimal(String binary,int i)
    {
        // If we reached last character
        int n = binary.length();
        if (i == n-1)
        return binary.charAt(i) - '0';
        
        // Add current tern and recur for
        // remaining terms
        return ((binary.charAt(i) - '0') << (n-i-1)) +
                toDecimal(binary, i+1);
    }
    
    // Driver code
    public static void main(String []args)
    {
        String binary = "1010";
        int i=0;
        System.out.println(toDecimal(binary,i));
        
    }

}

// This code is contributed 
// by ihritik ( Hritik Raj)

Python3

# Recursive Python3 program to convert 
# binary decimal 

def toDecimal(binary, i = 0):

    # If we reached last character 
    n = len(binary) 
    if (i == n - 1) :
        return int(binary[i]) - 0
    
    # Add current tern and recur for 
    # remaining terms 
    return (((int(binary[i]) - 0) << (n - i - 1)) + 
                        toDecimal(binary, i + 1))

# Driver code 
if __name__ == "__main__" :
    
    binary = "1010"
    print(toDecimal(binary))

# This code is contributed by Ryuga

// Recursive C# program to convert binary 
// decimal


using System;
class GFG
{
    static int toDecimal(string binary, int i=0)
    {
        // If we reached last character
        int n = binary.Length;
        if (i == n-1)
        return binary[i] - '0';
        
        // Add current tern and recur for
        // remaining terms
        return ((binary[i] - '0') << (n-i-1)) +
                toDecimal(binary, i+1);
    }
    
    // Driver code
    public static void Main()
    {
        string binary = "1010";
        Console.WriteLine(toDecimal(binary));
        
    }

}

// This code is contributed 
// by ihritik ( Hritik Raj)

PHP

<?php 
// Recursive CPP program to convert 
// binary decimal

function toDecimal($binary, $i = 0)
{
    // If we reached last character
    $n = strlen($binary);
    if ($i == $n - 1)
    return ord($binary[$i]) - ord('0');
    
    // Add current tern and recur for
    // remaining terms
    return ((ord($binary[$i]) - ord('0')) << ($n - $i - 1)) +
             toDecimal($binary, $i + 1);
}

// Driver code
$binary = "1010";
echo toDecimal($binary) . "\n";

// This code is contributed by ita_c
?>

JavaScript

<script>

// Recursive JavaScript program to convert binary 
// decimal

    function toDecimal(binary,i)
    {
        // If we reached last character
        let n = binary.length;
        if (i == n-1)
            return binary[i] - '0';
          
        // Add current tern and recur for
        // remaining terms
        return ((binary[i] - '0') << (n-i-1)) +
                toDecimal(binary, i+1);
    }
    
    // Driver code
    let binary = "1010";    
    let i=0;
    document.write(toDecimal(binary,i));
    


// This code is contributed by avanitrachhadiya2155

</script>

Output:

Time complexity: O(N) where N is the length of binary string
Auxiliary space: O(N) for recursive stack space.

C++ Program For Octal To Decimal Conversion

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Recursion

Recursive Program for Binary to Decimal

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