C Program to Convert Binary to Octal

#include <stdio.h>
#include <math.h>

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

    printf("Enter a binary number: ");
    scanf("%lld", &binaryNumber);

    printf("%lld in binary = %d in octal", binaryNumber, convertBinarytoOctal(binaryNumber));

    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: 101001
101001 in binary = 51 in octal