How can I loop through UITableView’s cells?

If you only want to iterate through the visible cells, then use

NSArray *cells = [tableView visibleCells];

If you want all cells of the table view, then use this:

NSMutableArray *cells = [[NSMutableArray alloc] init];
for (NSInteger j = 0; j < [tableView numberOfSections]; ++j)
{
    for (NSInteger i = 0; i < [tableView numberOfRowsInSection:j]; ++i)
    {
        [cells addObject:[tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:j]]];
    }
}

Now you can iterate through all cells:
(CustomTableViewCell is a class, which contains the property textField of the type UITextField)

for (CustomTableViewCell *cell in cells)
{
    UITextField *textField = [cell textField];
    NSLog(@"%@"; [textField text]);
}