IndexOutOfRangeException occured due to a ToCharArray() #

Question

I try to output the length of the longest possible sequence of 1s after flipping the second "0" of a given binary sequence. I think I've found the right algortithm for that but I keep struggling with an IndexOutOfRangeException

Here's my code

string b = Console.ReadLine();
    //char temp;
    int c = 0;
    int i = 0, l = 0, j = 0;
    l = b.Length - 1;
    char[] charArr = b.ToCharArray();
    while (l > 0)
    {
        if (charArr[i] == '0')
        {
            for (j = i; j <= l; j++)
            {
                c++;
                if (charArr[j] == '0')
                {

                    //temp = '1';
                    //char temp1 = temp;
                    charArr[j] = '1';

                }
            }
        }i++;
    }
    b = string.Join("", charArr);
    
    Console.WriteLine(c);