String array out of index C#

I am currently writing a little program that takes a string of numbers, splits them into lines and then writes them to a file. The problem is however all of my string arrays work just fine except this one and I cannot figure out why. The code is bellow and like I said I don’t get why sysid is failing since sysidpart works just fine.

string[] sysid;
string[] sysidpart;
sysid = new string[10];
sysidpart = new string[sysintcount];
while (H < sysintcount)
{
    sysidpart <mark>= syscode.Substring((H * 4), 4);</mark>

if (I == 0)
{
sysid[J] = sysidpart;
H++;
I++;
}
else if (I <= 3)
{
sysid[J] = sysid[J] + “-” + sysidpart;
H++;
I++;
}
else if (I == 4)
{
J++;
I = 0;
}
}

I figured out the issue, I put some print commands in the loop to see how it would turn out and it seemed that it was not having the error on the first loop but on a later one so I added in an extra zero to sysid and it works perfectly. Thank you for the help guys seems the error was on my end.