練習一:利用迴圈，將10張圖片顯示出來

<?php
if ($handle = opendir('images')) {
    while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != "..") {
            echo "<img src='images/$file'><br>";
        }
    }
    closedir($handle);
}
?>

利用練習一的檔案,只想顯示號碼是奇數(或偶數)的圖片

<?php
if ($handle = opendir('images')) {
    $i = 0;
    while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != "..") {
            if ($i % 2 === 0)
                echo "<img src='images/$file'><br>";
        }
        $i++;
    }
    closedir($handle);
}
?>

練習二:假設在 images 底下的圖片張數不清楚有幾張，請利用讀取檔案的方式,顯示全部的圖片

<?php
if ($handle = opendir('images')) {
    $fileArray = [];
    while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != "..") {
            array_push($fileArray, $file);
        }
    }
    closedir($handle);
    foreach ($fileArray as $file) {
        echo "<img src='images/$file' width=400><br>";
        echo "$file<br>";
    }
}
?>

• 利用練習二的檔案,將圖片寛度設為200px,再將圖片排列,一排有三張,將全部的圖片顯示,並在圖片下顯示圖片名稱

<?php
if ($handle = opendir('images')) {
    $fileArray = [];
    while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != "..") {
            array_push($fileArray, $file);
        }
    }
    closedir($handle);

    echo "<table>";
    for ($i=0; $i<count($fileArray); $i++) {
        if ($i % 3 === 0) {
            if ($i > 0) echo "</tr>";
            echo "<tr>";
        }
        echo "<td><img src='images/$fileArray[$i]' width=200><br>";
        echo "$fileArray[$i]</td>";
    }
    echo "</table>";
}
?>

• 進階練習:利用練習二的檔案，將圖片名稱由小到大(或由大到小),排列顯示

<?php
if ($handle = opendir('images')) {
    $fileArray = [];
    while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != "..") {
            array_push($fileArray, $file);
        }
    }
    closedir($handle);

    //升冪
    sort($fileArray);
    echo "<h2>由小排到大(升冪)</h2>";
    echo "<table>";
    for ($i=0; $i<count($fileArray); $i++) {
        if ($i % 3 === 0) {
            if ($i > 0) echo "</tr>";
            echo "<tr>";
        }
        echo "<td><img src='images/$fileArray[$i]' width=200><br>";
        echo "$fileArray[$i]</td>";
    }
    echo "</table>";

    //降冪
    rsort($fileArray);
    echo "<h2>由大排到小(降冪)</h2>";
    echo "<table>";
    for ($i=0; $i<count($fileArray); $i++) {
        if ($i % 3 === 0) {
            if ($i > 0) echo "</tr>";
            echo "<tr>";
        }
        echo "<td><img src='images/$fileArray[$i]' width=200><br>";
        echo "$fileArray[$i]</td>";
    }
    echo "</table>";
}
?>

練習三:分別將 images 底下的10張圖片取其中2張,存成 base64的格式到陣列中,另外產生名稱為 1 和2 的連結,點1會將陣列0的圖片顯示,點2會將陣列1的圖片顯示(註:陣列由0開始),請勿連結到 imges 底下的圖片

      這是圖片1的連結<a href='?img=1'>1</a>

      提示:在網址列  XXXXXX.php?img=1 ,在 php 內部 用$_GET['img'] 來取得變數的值

<?php
session_start();
if (!isset($_SESSION['images'])) {
    if ($handle = opendir('images')) {
        $fileArray = [];
        while (false !== ($file = readdir($handle))) {
            if ($file != "." && $file != "..") {
                array_push($fileArray, $file);
            }
        }
        closedir($handle);

        $count = count($fileArray);
        $images = [];
        $img_no = 2; //隨機選幾張圖
        for ($i=0; $i<$img_no; $i++) {
            while (in_array($file = $fileArray[rand(0, $count)], $images));
            $path = "images/$file";
            $type = pathinfo($path, PATHINFO_EXTENSION);
            $data = file_get_contents($path);
            $base64 = 'data:image/' . $type . ';base64,' . base64_encode($data);
            Array_push($images, $base64);
        }
        $_SESSION['images'] = $images;
    }
}
for ($i=1; $i<=count($_SESSION['images']); $i++)
    echo "<a href='?img=$i'>圖片$i</a> ";
echo "<br>";
if (!empty($_GET['img']))
    echo "<img src='" . $_SESSION['images'][$_GET['img']-1] . "'><br>";
?> 

1. 用遞迴寫出兩個正整數的最大公因數（gcd)
   gcd(144,128) 得到 ? gcd (742469137,283209877)得到?
   gcd(144,128) = 16
   gcd (742469137,283209877) = 7654321

   <?php
   function gcd($x, $y){
       if ($x === 0) return $y;
       if ($y === 0) return $x;
       if ($x >= $y) return gcd($y, $x % $y);
       else return gcd($y % $x, $x);
   }
   ?>
   <h1>最大公因數</h1>
   <form action="" method="post">
       <input type="text" name="num1">
       <input type="text" name="num2">
       <input type="submit" name="ok" value="送出">
   </form>
   <?php
   $num1 = !empty($_POST['num1'])?$_POST['num1']:0;
   $num2 = !empty($_POST['num2'])?$_POST['num2']:0;
   
   if ($num1>0 and $num2>0)
       echo "gcd($num1,$num2) = ".gcd($num1, $num2);
   ?>

2. 分別用for 迴圈，while 迴圈及遞迴寫出階乘計算
   並計算出10！=3628800

   <?php
   function fact($n){
       if ($n === 0 || $n === 1) return 1;
       else return $n*fact($n-1);
   }
   ?>
   <h1>階乘計算</h1>
   <form action="" method="post">
       <input type="text" name="num">
       <input type="submit" name="ok" value="送出">
   </form>
   <?php
   $num = !empty($_POST['num'])?$_POST['num']:'';
   if ($num === 0) echo "$num! = 1";
   elseif ($num > 0 && $num <= 170){
       //for 迴圈
       $sum = 1;
       for ($i=1; $i<=$num; $i++)
           $sum *= $i;
       echo "for 迴圈：$num! = $sum<br>";
   
       //while 迴圈
       $i = 1;
       $sum = 1;
       while($i<=$num){
           $sum *= $i;
           $i++;
       }
       echo "while 迴圈：$num! = $sum<br>";
   
       //遞迴
       echo "遞迴：$num! = ".fact($num)."<br>";
   }
   ?>

   （進階題：如何算出大數階乘?譬如300！?,提示：因數值很大，無法用實際的乘積來計算，建議用for 迴圈+對數，指數）

   <?php
   function fact($n){
       if ($n < 0) return -1;
       if ($n == 0 || $n == 1) return 1;
       $big[0] = 1;
       for ($i=2; $i<=$n; $i++){
           $carry = 0;
           $len = count($big);
           for ($j=0; $j<$len; $j++) {
               $total = $carry + $big[$j] * $i;
               if ($total > 0) {
                   $big[$j] = $total % 10;
                   $carry = ($total - $big[$j]) / 10;
               }
           }
           while($carry > 0){
               $len = count($big);
               $big[$len] = $carry % 10;
               $carry = ($carry - $big[$len]) / 10;
           }
       }
       return join("", array_reverse($big));
   }
   ?>

3. 一元二次方程式 a*x^2+b*x+c=0(次方^符號是借用basic 的表示方式，無關php)
   分別給 係數 a,b,c,請算出x 的解，如為虛數，請在虛數i表示
   例 a=1,b=-3,c=2,得 x1=2,x2=1

   <?php
   function caculate($a, $b, $c){
       if ($a == 0) return null;
       $delta = $b*$b - 4*$a*$c;
       $delta2 = sqrt(abs($delta));
       $x=[];
       if ($delta < 0) {
           array_push($x,(-$b/(2*$a)).'+'.($delta2/(2*$a)).'i');
           array_push($x,(-$b/(2*$a)).'-'.($delta2/(2*$a)).'i');
       }
       else {
           array_push($x,(-$b+$delta2)/(2*$a));
           array_push($x,(-$b-$delta2)/(2*$a));
       }
       return $x;
   }
   ?>
   <h1>一元二次方程式求解</h1>
   <form action="" method="post">
       <input type="text" name="a"> x^2 +
       <input type="text" name="b"> x +
       <input type="text" name="c"> = 0
       <input type="submit" name="ok" value="送出">
   </form>
   <?php
   $a = !empty($_POST['a'])?$_POST['a']:0;
   $b = !empty($_POST['b'])?$_POST['b']:0;
   $c = !empty($_POST['c'])?$_POST['c']:0;
   if ($a != 0 && $b && $c) {
           $x = caculate($a, $b, $c);
           echo "x1 = $x[0]<br>";
           echo "x2 = $x[1]<br>";
   }
   ?>

4. 費氏數列是很特別的數列，黃金比例，男星，自然界中的費氏數
   請列出1000下內的費氏數列

   <?php
   function fibonacci($n){
       if ($n === 0) return 0;
       if ($n === 1) return 1;
       return fibonacci($n-1) + fibonacci($n-2);
   }
   ?>
   <h1>費氏數列</h1>
   <form action="" method="post">
       <input type="text" name="num">
       <input type="submit" name="ok" value="送出">
   </form>
   <?php
   $num = !empty($_POST['num'])?$_POST['num']:'';
   if ($num >= 0) {
       echo "0";
       for ($i=1; ($f = fibonacci($i)) <= $num; $i++){
           echo ",$f";
       }
   }
   ?>