这个PHP（函数/构造？）做了什么，我在哪里可以找到更多的文档呢？

Simple question. Here is this code.

    $r = rand(0,1);
    $c = ($r==0)? rand(65,90) : rand(97,122);
    $inputpass .= chr($c);

I understand what it does in the end result, but I'd like a better explanation on how it works, so I can use it myself. Sorry if this is a bad question.

If you're unsure of what I'm asking about, its the (function?) used here:

$c = ($r==0)? rand(65,90) : rand(97,122);

That's called a ternary operator. It's effectively the equivalent of

if ($r == 0) {
    $c = rand(65, 90);
} else {
    $c = rand(97, 122);
}

But it's obviously a bit more compact. Check out the docs for more info.

That simply means:

if($r==0){
  $c = rand(65,90);
else{
  $c = rand(97,122);
}

If the statement is true the first operation after that ? is executed, else the operation after : is executed.

Its called a ternary operator.

Its the Ternary Operator

<?php
// Example usage for: Ternary Operator
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

// The above is identical to this if/else statement
if (empty($_POST['action'])) {
    $action = 'default';
} else {
    $action = $_POST['action'];
}

?>

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, and expr3 if expr1 evaluates to FALSE. Since PHP 5.3, it is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE, and expr3 otherwise.

It's called the ternary operator. It's similar to an if/else construct, but the difference is that an expression using the ternary operator yields a value.

That is, you can't set a variable to the result of an if/else construct:

// this doesn't work:
$c = if ($r == 0) {
         rand(65, 90);
     } else {
         rand(97, 122);
     }

You can read more about it here: http://php.net/ternary#language.operators.comparison.ternary

The ternary operator is frequently misused. There's little benefit to using it in the example you showed. Some programmers love to use compact syntactic sugar even when it's not needed. Or even when it's more clear to write out the full if/else construct.

The ternary operator can also obscure test coverage if you use a tool that measures lines of code covered by tests.