Generate Auto number Field in SharePoint list
To create auto generated list field do the following
1. Create a column field with data type number in the targeted list. For example I am creating an auto generated column Case ID.
First go to list settings-> Then in General settings go to Advanced Settings
3. In Advanced settings Click the radio button Yes , in Allow management of content types .And Click OK.
4. Now go to list settings again and a new Content types will be shown. In that click the Content type. In my case it is Item. Name may vary for you.
5. In that Content type all list columns will be shown. In that click the Case ID Column.
6. After that click the Hidden and then click OK
7. Then open SharePoint Designer create a new workflow for the list when a new item is created
8. And add update action to the list.
9. Click Add .In set this field value select Case ID
10. And for To this value select ID. Click OK and publish the workflow. Now a auto generated list column is created.