How do I validate textboxes in a datasource, windows form

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C#

WinForms

dataset

What is the easiest way to validate textboxes that need to be checked before they go through. I have 2 tables I have to insert my data into as well and that's just for one group, in total I have 3 groups but just a helpful tip towards the one will be fine.

I have the main table which is 'Person' and then 3 sub tables; 'Student', 'Teacher', 'Administration'.

Not all the textboxes need to be validated. (These two don't need to be validated sAdd2.Text and StudentType.Text).

//Edited

I'm now getting an error message with the "var pid = personTableAdapter..." with the var pid. "Embedded statement cannot be a declaration or labeled statement". Is this a decent way of trying to validate before it goes through to the database?
My normal code is

string errorMessage = "";

bool cancel = false;

if (string.IsNullOrEmpty(this.sFirstName.Text) || string.IsNullOrEmpty(this.sSurname.Text) || string.IsNullOrEmpty(this.sPhone.Text) || string.IsNullOrEmpty(this.sAdd1.Text) || string.IsNullOrEmpty(this.sSuburb.Text) || string.IsNullOrEmpty(this.sState.Text) || string.IsNullOrEmpty(this.sPostcode.Text));

//This control fails validation: Name cannot be empty.

if (cancel == true)

this.errorProvider1.SetError(sFirstName, "You must provide your first name");

errorMessage += "Enter your First name" + "/r/n";

this.errorProvider1.SetError(sSurname, "You must provide your surname");

errorMessage += "Enter your Surname" + "/r/n";

this.errorProvider1.SetError(sPhone, "You must provide your phone number");

errorMessage += "Enter your Phone number" + "/r/n";

this.errorProvider1.SetError(sAdd1, "You must provide your address");

errorMessage += "Enter your Address" + "/r/n";

this.errorProvider1.SetError(sSuburb, "You must provide your suburb");

errorMessage += "Enter your Suburb" + "/r/n";

this.errorProvider1.SetError(sState, "You must provide your state");

errorMessage += "Enter your State" + "/r/n";

this.errorProvider1.SetError(sPostcode, "You must provide your postcode");

errorMessage += "Enter your Postcode" + "/r/n";

if (cancel == false)

var pid = personTableAdapter.InsertPerson(sFirstName.Text, sSurname.Text, Convert.ToDateTime(sDoB.Text), sPhone.Text, sAdd1.Text, sAdd2.Text, sSuburb.Text, sState.Text, sPostcode.Text, StudentType.Text);

studentTableAdapter.Insert(Convert.ToInt32(pid), Convert.ToDateTime(sSDate.Text), sQCode.Text);

MessageBox.Show(sFirstName.Text + " " + sSurname.Text + " has been added. The Student ID is " + pid);

this.personTableAdapter.Fill(this._30002195DataSet.Person);

this.studentTableAdapter.Fill(this._30002195DataSet.Student);

this.Hide();

Admin f1 = new Admin();

f1.Show();

Thanks for your help! :)