Using PHP code in PHP code?

I have the following code in PHP:

<?php if (function_exists("insert_audio_player")) {insert_audio_player("[audio:|titles=]"} ?>

Which renders an audio player to my page in WordPress. I need to call a custom field inside this code. My custom field code is also coded in PHP:

<?php print_custom_field('tc_filename'); ?>

Something like:

<?php if (function_exists("insert_audio_player")) {insert_audio_player("[audio:<?php print_custom_field('tc_filename'); ?>|titles=<?php print_c开发者_如何学Goustom_field('tc_title'); ?>]"} ?>

How can I use or integrate the second block of code with the first?

---

<?php 
if (function_exists("insert_audio_player")) {
    insert_audio_player("[audio:".print_custom_field('tc_filename')."|titles=".print_custom_field('tc_title')."]"
} ?>

You can make this easier to read using sprintf()

<?php 
if (function_exists("insert_audio_player")) {
    insert_audio_player(sprintf(
        '[audio:%s|titles=%s]', 
        print_custom_field('tc_filename'), 
        print_custom_field('tc_title')
    ));
} 
?>    

Edit: based on your comment, the print_custom_field actually echo's the field, and doesn't return it, if there is no return function you can use, you need to use Output Buffering.

You can use a new function, which calls the print function but returns it instead of printing it to the screen:

function get_custom_field($field) {
    ob_start();
    print_custom_field($field);
    return ob_get_clean();
}

And use

<?php 
if (function_exists("insert_audio_player")) {
    insert_audio_player(sprintf(
        '[audio:%s|titles=%s]', 
        get_custom_field('tc_filename'), 
        get_custom_field('tc_title')
    ));
} 
?> 

---

Edit: As stated by the OP, the print_custom_field() function uses echo rather than return, so this answer will not work for this particular situation. See @Jacob's answer for a better solution.

Try this:

<?php
    if (function_exists("insert_audio_player")) {
        insert_audio_player(
            "[audio:" . print_custom_field('tc_filename') .
            "|titles=" . print_custom_field('tc_title') . "]"
        );
    }
?>

---

<?php if (function_exists("insert_audio_player")) {insert_audio_player("[audio:".function2()."|titles=".function3()."]"} ?>

then :

function function2()
{
print_custom_field('tc_filename');
}
function function3()
{
print_custom_field('tc_title');
}