How to implement proximity search with postcode? -

I have to use proximity search with postcode for Australia some links like

I know Let's see if I'm not mistaken, then I have to manage the post code with latitude and longitude. But I can not get it to apply. Can someone suggest me how to do this with php or give some links so that I can see more about it.

Thanks in advance

Edit:

I have edited my question:

Can I use the Google API for the given category I have found a link which is for Doppel, can I use the Google API to get the postcode only? The link has been followed

You must find a database that has longitude and latitude of each postal code. Once you have longitude and latitude, to calculate the distance between the points you will use the whwayen formula () To find proximity, you have to calculate the distance from your starting point to all points of your dataset. You can consider using a bounding box and then you can search for points within that bounding box. A geographical spatial database such as PostGIS has built in functions that can help with everyone.