Drupal – module for applying theme on particular pages

Greetings,
Hello,

Guys, I desire to affect another theme merely on particular pages (dissimilar from my major theme). I didn't discover a module to do that however i found some solutions on the net.

In fact I require to generate my own module and to penetrate a code.

So here is the issue that I don’t have any ideas on how to make it.

And here’s the code below which needs to be inserted.

function mymodule_init() {
// get global variable to override Drupal theme
global $custom_theme;
// check if the current page needs to have its to theme changed
if (stripos($_GET["q"],"admin/build/pages/") !== FALSE) {
// set the custom theme and initialize theme system
$custom_theme = 'garland';
init_theme();
}
}

Let me know where to place this code in the module.

Your help would be deeply appreciated,

Thank you