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 given octal number starting from right most 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. At 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

Below diagram explains how to convert octal number ( 123 ) to equivalent decimal value:

Below is the implementation of above idea.

C/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));
    }
}

// Contributed by Pramod Kumar


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 contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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