Program for Octal to Decimal Conversion

Last Updated : 12 May, 2021

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

Using predefined function

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

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

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