Impersonate user SystemAdmin Sharepoint Programmatically

Dim tempsite As SPSite = New SPSite("http://localhost/a")
Dim usertoken As SPUserToken = tempsite.SystemAccount.UserToken()

Using site As SPSite = New SPSite("http://localhost/a", usertoken)
Using oWebsite As SPWeb = site.OpenWeb()

'bla bla bla your code inside here

Check user permission Sharepoint programmatically

Public Function checkUserPermissionSP() As Boolean
Using site As SPSite = New SPSite("http://localhost/yoursite")

Using Web As SPWeb = site.OpenWeb()
If Web.DoesUserHavePermissions(SPBasePermissions.EnumeratePermissions) Then
Dim permissionToCheck As SPBasePermissions = SPBasePermissions.ManageLists
Console.WriteLine("The following users have {0} permission:", permissionToCheck)
Dim users As SPUserCollection = Web.Users
Dim user As SPUser
For Each user In users
Dim login As String = user.LoginName
If Web.DoesUserHavePermissions(login, permissionToCheck) Then
Console.WriteLine(login)
Return True
Else
Return False
End If
Next
Else : Return False
End If
End Using
End Using

End Function

Add User to Group Sharepoint programmatically (VB)

Public Function setPermissionSP() As Boolean
Using site As SPSite = New SPSite("http://localhost/blablabla")

Using oWebsite As SPWeb = site.OpenWeb()

Try

sUserId = "DOMAIN\USERID"
Try
oWebsite.AllowUnsafeUpdates = True
Dim usr As SPUser = oWebsite.EnsureUser(sUserId)
Dim grp As SPGroup = oWebsite.Groups("Group Name")

If usr Is Nothing Then
Return False
Else
If grp Is Nothing Then
Return False
Else
grp.AddUser(usr)
End If
End If

Catch ex As Exception
Throw New Exception(ex.Message)
Finally
oWebsite.AllowUnsafeUpdates = False

End Try

Return True

Catch ex As Exception

Throw New Exception(ex.Message)
End Try

End Using
End Using

End Function