Adding content type programatically

Scenario:
You want to add Content Type programatically

Solution:
SharePoint Object Model

Code:

using (SPSite site = new SPSite("http://localhost")) { 

using (SPWeb web = site.OpenWeb()) { 

SPContentType baseType = web.AvailableContentTypes["Document"];

 SPContentType proposal = new SPContentType( baseType, web.ContentTypes, "Project Proposal"); 

proposal.FieldLinks.Add(new SPFieldLink(web.AvailableFields["Author"])); 

web.ContentTypes.Add(proposal); 

}
}

Article: