Adding/Removing users to/from the group:

Note: We have to check before adding/removing users to/from the group and also check the users already exists or not in group. 
 

public void AddDeleteUsersInGroup(User user)         {             string GroupName = string.Empty;             if (user.IsAdmin.HasValue && user.IsAdmin.Value)                 GroupName = "Group Owners";             else if (user.IsApprover.HasValue && user.IsApprover.Value)                 GroupName = " Group Members";             else                 GroupName = " Group Visitors";             SPSecurity.RunWithElevatedPrivileges(delegate()             {                 using (SPSite site = new SPSite(SPContext.Current.Web.Url))                 {                     using (SPWeb web = site.OpenWeb())                     {                         try                         {                             web.AllowUnsafeUpdates = true;                             SPUser spUser = web.EnsureUser(user.UserName);                             if (spUser != null)                             {                                 SPGroup spGroup = spGatingGroup(web, GroupName);                                 if (spGroup != null && (IsUserInSPGroup(spUser, GroupName.Trim())))                                 {                                    //For adding user to the group                                       spGroup.AddUser(spUser);                                    //For removing user to the group                                     spGroup.RemoveUser(spUser);                                     spGroup.Update();                                 }                             }                         }                         catch (Exception ex)                         {                             throw ex;                         }                         finally                         {                             web.AllowUnsafeUpdates = false;                         }                     }                 }             });         }

 

private SPGroup spGatingGroup(SPWeb spDLRWeb, string groupName)         {             SPGroup spGroup = null;             try             {                 spGroup = spWeb.SiteGroups[groupName];                 if (spGroup == null) throw new Exception("Sharepoint Group name '" + groupName + "' not found");             }             catch (Exception ex)             {                 //ErrorHandling(ex);             }             return spGroup;         }

private bool IsUserInSPGroup(SPUser user, string strname)         {             foreach (SPGroup group in user.Groups)             {                 if (group.Name == strname)                     return true;             }             return false;         }