PHP:条件分岐
PHPのif文、switch文による条件分岐について学習した内容をまとめています。
条件に応じて処理をコントロールすることができれば、色々なことができるようになってくると思います。
if文
if文は、条件の値に応じて処理を行う条件判断文の一つ。
条件がtrueの際に一行だけ処理を行う場合は以下のように記述できる。
// 構文
if (条件)
//条件がtrueだった場合の処理;また、条件が複数の場合には以下のように記述できる。
// 構文
if (条件1) {
//条件1がtrueだった場合の処理;
} elseif(条件2) {
//条件2がtrueだった場合の処理;
} elseif(条件3) {
//条件3がtrueだった場合の処理;
} else {
//全ての条件がfalseだった場合の処理;
}使用してみる。
<?php
$num = 5;
if ($num == 10) {
print "10だと思う<br>";
} elseif($num == 5) {
print "5だと思う<br>";
} elseif($num == 1) {
print "1だと思う<br>";
} else {
print "どれでもないかも<br>";
}
//
//結果
// 5だと思う
//
?>別の記述方法もある。
// 構文
if (条件1) :
//条件1がtrueだった場合の処理;
elseif(条件2) :
//条件2がtrueだった場合の処理;
else :
//全ての条件がfalseだった場合の処理;
endif;switch文
switch文は、if文同様に条件の値に応じて処理を行う条件判断文の一つ。
式の評価がcaseの後の定数と一致すれば、breakまでの処理を実行する。
また、defaultは省略できる。
// 構文
switch(式) {
case 定数1:
//式の評価が定数1だった場合の処理;
break;
case 定数2:
//式の評価が定数2だった場合の処理;
break;
default:
//式の評価が定数1でも定数2でもなかった場合の処理;
break;
}breakを忘れてしまうと他のcase内の処理まで実行されてしまうため注意したい。
<?php
// breakを忘れると・・・
$num = 1;
switch($num) {
case 1:
print "break忘れてない、はず<br>";
//break;
case 2:
print "あれ、break忘れてるって<br>";
break;
default:
print "何が起こった";
break;
}
//
//結果
// break忘れてない、はず
// あれ、break忘れてるって
//
?>別の記述方法もある。
// 構文
switch(式) :
case 定数1:
//式の評価が定数1だった場合の処理;
break;
case 定数2:
//式の評価が定数2だった場合の処理;
break;
default:
//式の評価が定数1でも定数2でもなかった場合の処理;
break;
endswitch;三項演算子
簡単な条件判断ならば、三項演算子「?:」を使って記述できる。
// 構文
(条件) ? trueの式 : falseの式 ;if文と比べてみる。
<?php
$num = 1;
//if文
if ($num == 1):
print "1だね<br>";
else:
print "1じゃないね<br>";
endif;
//三項演算子
print ($num == 1) ? "1だね<br>" : "1じゃないね<br>";
//結果
// 1だね
// 1だね
?>その他の記事
作成日：2018/07/31
更新日：2018/08/16
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