Convert Octal to Decimal - Tutorial [Updated]

Problem Statement: Given an Octal Number, convert it into a Decimal Number.

Examples:

Example 1:
Input: 345
Output: 229
Explanation: Decimal equivalent of given Octal expressionis 229

Example 2:
Input: 170
Output: 121
Explanation: Decimal equivalent of given Octal expression is121

Solution

Disclaimer: Don’t jump directly to the solution, try it out yourself first.

Approach:

In Octal to Decimal Conversion, We will take every digit of the number and multiply it with 8 raised to power i which will increase by 1 when we move to the next digit and then add it to sum. This task is repeated until n becomes 0.

For Eg, 345

Step 1: Take digit 5, multiply 8 raised to power 0 with it so we get 5 here and now n becomes 34

Step 2: Take digit 4, multiply 8 raised to power 1 with it so we get 32 and add it to the sum which now becomes 37. Also, n becomes 3.

Step 3: Take digit 3 and multiply 8 raised to power 2 with it so we get 192 and add it to sum which now becomes 229. Now n becomes zero.

Code:

C++ Code

#include <iostream>
#include <math.h>
using namespace std;
int OctaltoDecimal(int Octal)
{
  int Decimal = 0;
  int i = 0;
  while (Octal != 0)
  {
    int rem = Octal % 10;
    Decimal += rem * pow(8, i);
    i++;
    Octal /= 10;
  }
  return Decimal;
}
int main()
{
  int Octal = 345;
  cout <<"The decimal equivalent of the given octal number is "<<OctaltoDecimal(Octal) << endl;
  return 0;
}

Output:

The decimal equivalent of the given octal number is 229

Time Complexity: O(n) where n is the number of digits in the Octal Number.

Space Complexity: O(1)

Java Code

import java.util.*;
public class Main {
  public static int OctaltoDecimal(int Octal) {
    int Decimal = 0;
    int i = 0;
    while (Octal != 0) {
      int rem = Octal % 10;
      Decimal += rem * Math.pow(8, i);
      i++;
      Octal /= 10;
    }
    return Decimal;
  }
  public static void main(String[] args) {
    int Octal = 345;
    System.out.println("The decimal equivalent of the given octal number is 
    "+OctaltoDecimal(Octal));
  }
 
}

Output:

The decimal equivalent of the given octal number is 229

Time Complexity: O(n) where n is the number of digits in the Octal Number.

Space Complexity: O(1)

Special thanks to Gurmeet Singh for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article