Add an Adsense banner to your wordpess site without plugin

1. Start a FTP program and connect to your wordpress website
2. Locate your funtions.php (wp-content\themes\theme_name\functions.php)
3. Edit the file and put the following code in your functions.php file:

function showads() {
return '
<script type="text/javascript"><!--
google_ad_client = "ca-pub-3134535021136249";
google_ad_slot = "3483719222";
google_ad_width = 468; google_ad_height = 60;
// -->
</script>
<script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
';}
add_shortcode('banner', 'showads');

4. Modify the client, slot, width and height values
5. Safe the file and overwrite the current

Now you can use the [banner] tag in your post to publish the banner:

[banner]