C# code to create Site Column, Content Type, and add fields to Content Type

You can use below code to create following:-
1. Site Columns
2. Content Types
3. Add Fields to Content Type

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using Microsoft.SharePoint; namespace LAB {     public static class SPDevUtility     {         public static SPContentType CreateSiteContentType(SPWeb web, string contentTypeName,         SPContentTypeId parentItemCTypeId, string group)         {             if (web.AvailableContentTypes[contentTypeName] == null)             {                 SPContentType itemCType = web.AvailableContentTypes[parentItemCTypeId];                 SPContentType contentType =                     new SPContentType(itemCType, web.ContentTypes, contentTypeName) { Group = @group };                 web.ContentTypes.Add(contentType);                 contentType.Update();                 return contentType;             }             return web.ContentTypes[contentTypeName];         }         public static SPField CreateSiteColumn(SPWeb web, string displayName,             SPFieldType fieldType, string groupDescriptor)         {             if (!web.Fields.ContainsField(displayName))             {                 string fieldName = web.Fields.Add(displayName, fieldType, false);                                 SPField field = web.Fields.GetFieldByInternalName(fieldName);                                 field.Group = groupDescriptor;                                 field.Update();                 return field;             }             return web.Fields[displayName];         }         public static void AddFieldToContentType(SPWeb web, SPContentTypeId contentTypeId, SPField field)         {             SPContentType contentType = web.ContentTypes[contentTypeId];             if (contentType == null) return;             if (contentType.Fields.ContainsField(field.Title)) return;             SPFieldLink fieldLink = new SPFieldLink(field);             contentType.FieldLinks.Add(fieldLink);             contentType.Update();         }     } }