C++ Program For Octal To Decimal Conversion

Last Updated : 03 Jul, 2023

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

Examples:

Input : 67
Output: 55

Input : 512
Output: 330

Input : 123
Output: 83

1. Simple Approach

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.

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:

Flowchart for octal to decimal conversion

Below is the implementation of the 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 code
int main()
{
    int num = 67;
 
    cout << octalToDecimal(num) << endl;
}

Output

The complexity of the above method

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

Auxiliary space: O(1)

2. Using Predefined stoi() Function

Below is the C++ program for Octal to Decimal Conversion:

C++

// C++ program to convert octal 
// to decimal
#include <iostream>
using namespace std;
int OctToDec(string n) 
{ 
  return stoi(n, 0, 8); 
}
 
// Driver code
int main()
{
 
  string n = "67";
  cout << OctToDec(n);
  return 0;
}
 
// This code is contributed by phasing17

Output

Please refer complete article on Program for Octal to Decimal Conversion for more details!

C++ Program For Hexadecimal To Decimal Conversion

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C++ Program For Octal To Decimal Conversion

1. Simple Approach

C++

The complexity of the above method

2. Using Predefined stoi() Function

C++

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