You're never constructing and assigning the variable itself - but you try to use the array:
// Need to add:
pntrs = new int[Pntrnum];
for (int i = 0; i < Pntrnum; i++)
{
stream.Position = Pntrstrt;
stream.Read(data, 0, data.Length);
pntrs[i] = BitConverter.ToInt32(data, 0);
}
// Need to add:
Strs = new string[Pntrnum];
for (int i = 0; i < Pntrnum; i++)
{
byte[] sttrings = new byte[pntrs[i + 1] - pntrs[i]];
stream.Position = pntrs[i];
stream.Read(sttrings, 0, sttrings.Length);
Strs[i] = Encoding.GetEncoding("SHIFT-JIS").GetString(sttrings);