vm.RegisterCommand('+', v => Inc(v));
private static void Inc(IVirtualMachine v)
{
    if (v.Memory[v.MemoryPointer] == (char)255)
        v.Memory[v.MemoryPointer] = (char)0;
    else
        v.Memory[v.MemoryPointer]++;
}

vm.RegisterCommand('+', b => (b.Memory[b.MemoryPointer] == 255) ? 1 : 2 );