Binary To Decimal Program Help

// Arrays may not be used to contain the binary digits entered by the user

// Determining the decimal equivalent of a particular binary digit in the sequence must be calculated using a single mathematical function,
// for example the natural logarithm. It's up to you to figure out which function to use.

//  User can enter up to 8 binary digits in one input field
//  User must be notified if anything other than a 0 or 1 was entered
//  User views the results in a single output field containing the decimal (base 10) equivalent of the binary number that was entered

// int numberInput = 0;
Console.WriteLine("Input up to 8 binary digits: ");
String userInput = Console.ReadLine();
// bool isParseable = Int32.TryParse(userInput, out numberInput);
int index = 0;
int finalResult = 0;

for (int i=0; i < userInput.Length; i++)
{
    if (userInput[i] = "0")
    {
        GetPow(2, index);
        finalResult += index;
        System.Console.WriteLine(finalResult);
        index++;
    }
}

static int GetPow(int baseNum, int powNum)
{
    int result = 1;

    for (int i = 0; i < powNum; i++)
    {
        result = result * baseNum;
    }

    return result;
}