C Program to Convert Octal to Binary

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

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

    printf("Enter an octal number: ");
    scanf("%d", &octalNumber);

    printf("%d in octal = %lld in binary", octalNumber, convertOctalToBinary(octalNumber));

    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: 67
67 in octal = 110111 in binary