C++ Program to Convert Binary Number to Octal and vice-versa

In this example, you will learn to convert binary number to octal, and octal number to binary manually by creating a user-defined function.

Example 1: Program to Convert Binary to Octal

In this program, we will first convert the binary number to decimal. Then, the decimal number is converted to octal.

#include <iostream>
#include <cmath>

using namespace std;

int convertBinarytoOctal(long long);
int main()
{
    long long binaryNumber;

    cout << "Enter a binary number: ";
    cin >> binaryNumber;

    cout << binaryNumber << " in binary = " << convertBinarytoOctal(binaryNumber) << " in octal ";

    return 0;
}

int convertBinarytoOctal(long long binaryNumber)
{
    int octalNumber = 0, decimalNumber = 0, i = 0;

    while(binaryNumber != 0)
    {
        decimalNumber += (binaryNumber%10) * pow(2,i);
        ++i;
        binaryNumber/=10;
    }

    i = 1;

    while (decimalNumber != 0)
    {
        octalNumber += (decimalNumber % 8) * i;
        decimalNumber /= 8;
        i *= 10;
    }

    return octalNumber;
}

Output

Enter a binary number: 10001
10001 in binary = 21 in octal

The binary number entered by the user is passed to convertBinaryToOctal() function. And, this function converts the number to octal and returns to the main() function


Example 2: Program to Convert Octal to Binary

In this program, the octal number is converted to decimal at first. Then, the decimal number is converted to binary number.

#include <iostream>
#include <cmath>

using namespace std;

long long convertOctalToBinary(int);
int main()
{
    int octalNumber;

    cout << "Enter an octal number: ";
    cin >> octalNumber;

    cout << octalNumber << " in octal = " << convertOctalToBinary(octalNumber) << "in binary";

    return 0;
}

long long convertOctalToBinary(int octalNumber)
{
    int decimalNumber = 0, i = 0;
    long long binaryNumber = 0;

    while(octalNumber != 0)
    {
        decimalNumber += (octalNumber%10) * pow(8,i);
        ++i;
        octalNumber/=10;
    }

    i = 1;

    while (decimalNumber != 0)
    {
        binaryNumber += (decimalNumber % 2) * i;
        decimalNumber /= 2;
        i *= 10;
    }

    return binaryNumber;
}

Output

Enter an octal number: 54
54 in octal = 101100

The octal number entered by the user is passed to convertOctalToBinary() function. And, this function converts the number to binary and returns the main() function