Exception at byte arithmetic

Question

Im trying to get all bytes from a jpg file and manipulate it just as a fun practice. im getting each byte and subtracting it from 1 and then add that result to another byte array

    byte[] f = File.ReadAllBytes("aaa.jpg");
    byte[] fo = null;
    for(int i = 0;i<=f.Length;i++)
    {
        fo[i] = (byte)(f[i] - 1);
    }
    MessageBox.Show("done");

but im getting an error : Object reference not set to an instance of an object. its on line 5 and i don't really understand whats the problem

`byte[] fo = f.Select(b => unchecked((byte) (b - 1))).ToArray();`; `unchecked` - if you want to turn `00` into `FF` silently (without `OverflowException`) — Dmitry Bychenko, Mar 11 '17 at 22:28

score 0 · Accepted Answer · answered Mar 11 '17 at 22:22

You need to instantiate fo byte[] array. At the first iteration of your loop, you are accessing indexer property. Since indexer property belongs to an object, you are getting Object reference null exception, because array isn't instantiated.

byte[] fo = new byte[f.Length];

Exception at byte arithmetic

1 Answers1