PHP条件语句？

First, I would like to say that I'm not the greatest PHP developer. That being said, I would like some input on my code. I spent an hour trying to get this to work and I finally got it to work, however, I would like to know if this is the best way to do it. I'm asking the community because I'm trying to become a better developer.

I'm building a search form that uses POST method to send values to a search page. This page then takes the values, checks the conditional statements, and updates the query based on the results.

Here is my code.

Search form code

echo '<form method="post" class="cat-search" action="'.esc_url( home_url( '/search' ) ).'" role="search" >
            <div class="gender-fields">
                <span class="label-wrap">
                    <input type="radio" name="gender" value="male" id="male">
                    <label for="male">Male</label>
                </span>
                <span class="label-wrap">
                    <input type="radio" name="gender" value="female" id="female">
                    <label for="female">Female</label>
                </span>
                <span class="label-wrap">
                    <input type="radio" name="gender" value="" id="both">
                    <label for="both">Both</label>
                </span>
            </div>
            <select class="cat-letters" name="letter">
             <option value="">Search by letter</option>';
            foreach ( $categories as $category ) {
                echo'<option value="'.$category->slug.'">'.$category->name.'</option>';
            }
            echo '</select>
            <input class="search-submit" value="Search" type="submit" />
        </form>';

Search page conditional code

$let = esc_html($_POST["letter"]);
$gen = esc_html($_POST["gender"]);


if ( !empty($_POST["gender"]) && !empty($_POST["letter"])) {
    $cat_array = array($let,$gen);
    $cat_string = implode("+", $cat_array);
} else if ( empty($_POST["gender"] ) ) {
    $cat_string = $let;
} else {
    $cat_string = $gen;
}

First, I tried to use the isset() function instead of empty(), but I just couldn't get it to work.

Is this the right way to do it, or is there a better way to achieve the same results?

*I never had a problem with the form, the problem was with the conditional statements.

I would just recommend using isset here

$let = esc_html(isset($_POST["letter"]) ? $_POST['letter'] : '');
$gen = esc_html(isset($_POST["gender"]) ? $_POST['gender'] : '');

So you don't have any PHP errors when there are not letter and gender parameters received ;)

Read more about ternay operators here

It is good practice to avoid using GLOBAL variables directly, get a temp variable instead.

$post = $_POST;
$let = esc_html(isset($post['letter']) ? $post['letter'] : '');

With PHP 7, you can use operator ?? no need to check for undefined index:

$let = esc_html($post['letter'] ?? '');

Also use (single)'' over (double)"" quotes wherever possible, and check for whitespaces by trimming

Before PHP 7:

$post = $_POST;
$cat_array = array();
foreach(array('letter','gender') as $field){
    if(isset($post[$field]) && trim(esc_html($post[$field]))){
       array_push($cat_array,esc_html($post[$field]));
    }
}
$cat_str = implode('+',$cat_array);

1. Why did you add the trim() in the if statement?

What if user inputs only whitespaces? Your code will allow it and which defeats validation process.

2. How is it that if only one field is selected the implode function doesn't add a + at the end? Is it because it's an array?

Yes, implode() will join/concat two or more elements of array.

First of all, it is not a good practice to write the HTML contents using PHP. Try to separate the HTML from PHP in your HTML form as follows.

<form method="post" class="cat-search" action="<?php echo esc_url(home_url( '/search' ));?>" role="search" >
            <div class="gender-fields">
                <span class="label-wrap">
                    <input type="radio" name="gender" value="male" id="male">
                    <label for="male">Male</label>
                </span>
                <span class="label-wrap">
                    <input type="radio" name="gender" value="female" id="female">
                    <label for="female">Female</label>
                </span>
                <span class="label-wrap">
                    <input type="radio" name="gender" value="" id="both">
                    <label for="both">Both</label>
                </span>
            </div>
            <select class="cat-letters" name="letter">
             <option value="">Search by letter</option>
             <?php foreach ( $categories as $category ) { ?>
                <option value="<?php echo $category->slug;?>"><?php echo $category->name;?></option>
            <?php } ?>
            </select>
            <input class="search-submit" value="Search" type="submit" />
        </form>

And then the Search page conditional code

$let = trim(esc_html($_POST["letter"]));
$gen = trim(esc_html($_POST["gender"]));


if ($let != "" && $gen != "") {
    $cat_array = array($let,$gen);
    $cat_string = implode("+", $cat_array);
} else if ($let != "") {
    $cat_string = $let;
} else {
    $cat_string = $gen;
}