给定一个表达式的输入，该表达式由一串字母和运算符（加号、减号和字母。IE：'b-d+e-f'）和一个包含一组以逗号分隔的变量/值对的文件（即：a=1,b=7,c=3,d=14）编写一个程序，输出输入表达式的结果。
例如，如果表达式输入为 ("a + b+c -d") 并且文件输入为 (a=1,b=7,c=3,d=14)，则输出将为 -3。
到目前为止，我得到了这个，它计算了数字，但不知道如何用字母 abcd 来计算它，
<html>
<head>
</head>
<body>
<form action = "" method = "GET">
Number 1: <input type = "text" name = "input[]" size=3>
<br/>
Number 2: <input type = "text" name = "input[]" size=3> <br>
Number 3: <input type = "text" name = "input[]" size=3> <br>
Number 4: <input type = "text" name = "input[]" size=3> <br>
<input type="hidden" name="calc" value ="yes">
<input type = "submit" name = "Calculate"/>
</form>
</body>
</html>
<?php
print_r($_GET);
$myInputs = $_GET['input'];
print_r($myInputs);
$myArray = array();
$myArray['a'] = 5;
$myArray['b'] = 10 ;
$myArray['c'] = 15 ;
$myArray['d'] = 20 ;
echo $myArray[$_GET['a']] + $myArray[$_GET['b']] ;
/*
if ($_GET['calc'] == "yes")
{
$a = $_GET['a'];
$b = $_GET['b'];
$c = $_GET['c'];
$d = $_GET['d'];
$total = $a+$b+$c+$d;
print "Total is: $total <p>";
}
*/
?>
<?php
$expression = '';
$input = array( 'a' => 5,
'b' => 10,
'c' => 15,
'd' => 20);
$total = 0;
$sum = '';
// Override default expression and input values
if(isset($_POST['Calculate']))
{
$input = $_POST['input']; //input being passed via POST method
$expression = $_POST['expression']; //expression being passed via POST method
}
// make sure the users expression is safe to use
if(preg_match('#^[a-z+-\s]+$#i', $expression))
{
$sum = $expression; //evaluates sum as expression
$input_letters = array(); //puts letters into a array
$input_operators = array(); //puts operators into a array
for ($i = 0; $i < strlen($expression) ; $i++) { //gets string length
if (($i % 2) == 0) {
$input_letters[] = $expression[$i]; //getting the character for the position i
} else {
$input_operators[] = $expression[$i];
}
}
//
for ($i = 0 ; $i < sizeof($input_letters); $i++) { //size of= numbers (4)
$value = $input[$input_letters[$i]]; //takes the value from the letters
if ($i == 0) {
$sum += $value; //adds the sum if = 0
} else {
if ($input_operators[$i-1] == '+') { //checks to see if the operator is +
$sum += $value;
} else if ($input_operators[$i-1] == '-') { //checks to see if the operator is -
$sum -= $value;
}
}
print_r($value);
}
} else {
echo "Error: expression not correct form"; //error message
}
?>
<form action="" method="post"> <!--Form begins-->
Number A: <input type="text" name="input[a]" value="<?php echo $input['a']; ?>" size=3> <br/>
Number B: <input type="text" name="input[b]" value="<?php echo $input['b']; ?>" size=3> <br>
Number C: <input type="text" name="input[c]" value="<?php echo $input['c']; ?>" size=3> <br>
Number D: <input type="text" name="input[d]" value="<?php echo $input['d']; ?>" size=3> <br>
<br>
Expression: <input type = "text" name = "expression" value="<?php echo $expression ?>"> =
<?php echo $sum; ?><br>
Sum: <?php echo $sum; ?><br>
<input type="submit" name="Calculate" />
</form>
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script>
$( "form" ).submit(function( event ) {
var val_is_good=($('input[name="expression"]').val().length==4)?true:false;
if(!val_is_good){alert('Enter four letters or die!');}
});
</script>
现在我添加了一个脚本来告诉用户如果他们输入超过 4 个字母，则警告消息说请只输入四个字母，有人知道为什么我的脚本即使只输入四个字母也会输出警告消息？