Program for Octal to Decimal Conversion

Given an octal number as input, we need to write a program to convert the given octal number into equivalent decimal number.

Examples:

Input : 67
Output: 55

Input : 512
Output: 330

Input : 123
Output: 83

The idea is to extract the digits of a given octal number starting from the rightmost digit and keep a variable dec_value. At the time of extracting digits from the octal number, multiply the digit with the proper base (Power of 8) and add it to the variable dec_value. In the end, the variable dec_value will store the required decimal number.

For Example: 

If the octal number is 67. 

dec_value = 6*(8^1) + 7*(8^0) = 55

The below diagram explains how to convert an octal number (123) to an equivalent decimal value:  

Below is the implementation of above idea. 

C++

// C++ program to convert octal to decimal
#include <iostream>
using namespace std;

// Function to convert octal to decimal
int octalToDecimal(int n)
{
    int num = n;
    int dec_value = 0;

    // Initializing base value to 1, i.e 8^0
    int base = 1;

    int temp = num;
    while (temp) {

        // Extracting last digit
        int last_digit = temp % 10;
        temp = temp / 10;

        // Multiplying last digit with appropriate
        // base value and adding it to dec_value
        dec_value += last_digit * base;

        base = base * 8;
    }

    return dec_value;
}

// Driver program to test above function
int main()
{
    int num = 67;

    cout << octalToDecimal(num) << endl;
}

Java

// Java program to convert octal to decimal
import java.io.*;

class GFG {

    // Function to convert octal to decimal
    static int octalToDecimal(int n)
    {
        int num = n;
        int dec_value = 0;

        // Initializing base value to 1, i.e 8^0
        int base = 1;

        int temp = num;
        while (temp > 0) {
            // Extracting last digit
            int last_digit = temp % 10;
            temp = temp / 10;

            // Multiplying last digit with appropriate
            // base value and adding it to dec_value
            dec_value += last_digit * base;

            base = base * 8;
        }
        return dec_value;
    }

    // driver program
    public static void main(String[] args)
    {
        int num = 67;
        System.out.println(octalToDecimal(num));
    }
}

// This code is contributed
// by Pramod Kumar

Python3

# Python3 program to convert
# octal to decimal

# Function to convert
# octal to decimal


def octalToDecimal(n):

    num = n
    dec_value = 0

    # Initializing base value
    # to 1, i.e 8^0
    base = 1

    temp = num
    while (temp):

        # Extracting last digit
        last_digit = temp % 10
        temp = int(temp / 10)

        # Multiplying last digit
        # with appropriate base
        # value and adding it
        # to dec_value
        dec_value += last_digit * base

        base = base * 8

    return dec_value


# Driver Code
num = 67
print(octalToDecimal(num))

# This code is contributed by mits

C#

// C# program to convert octal to
// decimal
using System;

class GFG {

    // Function to convert octal
    // to decimal
    static int octalToDecimal(int n)
    {
        int num = n;
        int dec_value = 0;

        // Initializing base value
        // to 1, i.e 8^0
        int b_ase = 1;

        int temp = num;
        while (temp > 0) {

            // Extracting last digit
            int last_digit = temp % 10;
            temp = temp / 10;

            // Multiplying last digit
            // with appropriate base
            // value and adding it to
            // dec_value
            dec_value += last_digit * b_ase;

            b_ase = b_ase * 8;
        }
        return dec_value;
    }

    // driver program
    public static void Main()
    {
        int num = 67;

        Console.WriteLine(octalToDecimal(num));
    }
}

// This code is contributed by vt_m.

PHP

<?php
// PHP program to convert octal to decimal

// Function to convert
// octal to decimal
function octalToDecimal($n)
{

    $num = $n;
    $dec_value = 0;

    // Initializing base value
    // to 1, i.e 8^0
    $base = 1;

    $temp = $num;
    while ($temp)
    {

        // Extracting last digit
        $last_digit = $temp % 10;
        $temp = $temp / 10;

        // Multiplying last digit
        // with appropriate base
        // value and adding it
        // to dec_value
        $dec_value += $last_digit * $base;

        $base = $base * 8;
    }

    return $dec_value;
}

    // Driver Code
    $num = 67;
    echo octalToDecimal($num);

// This code is contributed by anuj_67
?>

Javascript

<script>

// JavaScript program to convert octal to decimal

// Function to convert octal to decimal
function octalToDecimal(n)
{
    let num = n;
    let dec_value = 0;

    // Initializing base value to 1, i.e 8^0
    let base = 1;

    let temp = num;
    while (temp) {

        // Extracting last digit
        let last_digit = temp % 10;
        temp = Math.floor(temp / 10);

        // Multiplying last digit with appropriate
        // base value and adding it to dec_value
        dec_value += last_digit * base;

        base = base * 8;
    }

    return dec_value;
}

// Driver program to test above function

    let num = 67;

    document.write(octalToDecimal(num) + "<br>");


// This code is contributed by Surbhi Tyagi

</script>

Output

55

Using predefined function

C++

// C++ program to convert octal to decimal
#include <iostream>
using namespace std;
int OctToDec(string n)
{
  return stoi(n, 0, 8);
}
int main()
{

  string n = "67";
  cout << OctToDec(n);
  return 0;
}

// This code is contributed by phasing17

Java

// Java program to convert octal to decimal
import java.io.*;

class GFG {
    public static int OctToDec(String n)
    {
        return Integer.parseInt(n, 8);
    }
    public static void main(String[] args)
    {

        String n = "67";
        System.out.println(OctToDec(n));
    }
}

Python3

# Python program to convert octal to decimal
def OctToDec(n):
    return int(n, 8);

if __name__ == '__main__':

    n = "67";
    print(OctToDec(n));

# This code is contributed by 29AjayKumar

C#

using System;

public class GFG{

    public static int OctToDec(String n)
    {
        return Convert.ToInt32(n, 8);
    }

    static public void Main (){

        string n = "67";
        Console.WriteLine(OctToDec(n));
    }
}

// THIS CODE IS CONTRIBUTED BY RAG2127

Javascript

<script>
// javascript program to convert octal to decimal
   function OctToDec(n)
    {
        return parseInt(n, 8);
    }

   var n = "67";
   document.write(OctToDec(n));
// This code contributed by Princi Singh
</script>

Output

55

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