Add number in increment of one to DIV ID

Question

I'm using a shortcode to display a custom post type. The shortcode contains an attribute to display only posts of a specific category within the custom post type e.g. [faq category="travel"]

For each shortcode wordpress outputs a specific set of html, including a div with id of "faq-accordion". For each shortcode I need to output the div with ID "faq-accordion+1" e.g "faq-accordion1", "faq-accordion2", "faq-accordion3", etc.

I have managed to append a number to each div but for some reason it only goes as far as 6 and then repeats the numbers.

Here is my code

    add_shortcode( 'faq', 'wpse105856_shortcode_callback' );

    function wpse105856_shortcode_callback( $atts ) {
    extract( shortcode_atts( array(
        'category' => ''
    ), $atts ) );

    $args = array(
        'numberposts' => -1,
        'orderby' => 'menu_order',
        'order' => 'ASC',
        'post_type' => 'faq'
    );

      if ( ! empty( $category ) ) {
        $args['category_name'] = $category;
    };

    $posts = get_posts( $args );

    //Here is where I am trying to dynamically add a new number to the faq-accordion div
    $num = 0;

        foreach ( $posts as $post ) {   
    $faq  = '<div id="faq-accordion'.++$num.'">'; //Open the container
        };

    foreach ( $posts as $post ) { // Generate the markup for each Question
        $faq .= sprintf(('<h3><a href="">%1$s</a></h3><div>%2$s</div>'),
            $post->post_title,
            wpautop($post->post_content)
        );
    };
    $faq .= '</div>'; //Close the container

    return $faq; //Return the HTML.
};

Answer 1

the code should be instead

add_shortcode( 'faq', 'wpse105856_shortcode_callback' );

function wpse105856_shortcode_callback( $atts ) {
extract( shortcode_atts( array(
    'category' => ''
), $atts ) );

$args = array(
    'numberposts' => -1,
    'orderby' => 'menu_order',
    'order' => 'ASC',
    'post_type' => 'faq'
);

if ( ! empty( $category ) ) {
    $args['category_name'] = $category;
};

$posts = get_posts( $args );

//Here is where I am trying to dynamically add a new number to the faq-accordion div
$num = 0;
$faq = '';
$faq = '<div class="question-wrapper">';//wrapper div for all the questions
//Generate div for each question
foreach ( $posts as $post ) {   
    $faq  .= '<div id="faq-accordion'.++$num.'">'; //Open the container
    // Generate the markup for each Question
    $faq .= sprintf(('<h3><a href="">%1$s</a></h3><div>%2$s</div>'),
        $post->post_title,
        wpautop($post->post_content)
    );
    $faq .= '</div>'; //Close the container
}
$faq .= '</div>';//close the wrapper

return $faq; //Return the HTML.
};

As you commented, for your need in comment you can use $post->ID in div id like

echo '<div id="'.$post->ID.'">';