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Program for Octal to Decimal Conversion

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  • Difficulty Level : Easy
  • Last Updated : 25 Sep, 2022
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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

Time complexity: O(logN) where N is the given number
Auxiliary space: O(1)

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

 

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 


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