根據欄位個數，迴圈列印字母排序，使用於PHPExcel

最後拼裝成陣列

$tableheader = array('ID','學籍ID','退費單號','真實姓名','性別','手機號','QQ','Email','身份證號',
'專案型別','報讀院校','報讀專業','專業層次','報讀班型','利息費','管理費','課時費','退費金額',
'扣款單編號','扣款單開單人/申請人','退費理由','扣款單開單校區','面諮校區','面諮老師','TMK 老師','所屬事業部','所屬團隊','事業部稽核','備註','分校稽核','備註','教務稽核','備註','財務稽核','備註'
 
,'退費狀態',
'收款開戶人姓名','收款開戶銀行','收款銀行賬號','收款備註','建立時間','退費備註');

// 根據欄位個數，設定表頭排序字母
$letter_str = '';
for($i='A',$k=0; $i<='Z'; $i++,$k++){
    if($k == count($tableheader)){
        break;
    }

    // 最後一個取消逗號
    if($k == (count($tableheader)-1)){
        $letter_str .= $i;
    } else {
        $letter_str
 
 .= $i.',';
    }
}

$letter = explode(',', $letter_str);
print_r($letter);

輸出拼裝成陣列

Array
(
    [0] => A
    [1] => B
    [2] => C
    [3] => D
    [4] => E
    [5] => F
    [6] => G
    [7] => H
    [8] => I
    [9] => J
    [10] => K
    [11] => L
    [12] => M
    [13
 
] => N
    [14] => O
    [15] => P
    [16] => Q
    [17] => R
    [18] => S
    [19] => T
    [20] => U
    [21] => V
    [22] => W
    [23] => X
    [24] => Y
    [25] => Z
    [26] => AA
    [27] => AB
    [28] => AC
    [29] => AD
    [30] => AE
    [31] => AF
    [32] => AG
    [33] => AH
    [34] => AI
    [35] => AJ
    [36] => AK
    [37] => AL
    [38] => AM
    [39] => AN
    [40] => AO
    [41] => AP
)