Validate All Text Boxes In PlaceHolder

I've problem with validating all text boxes in PlaceHolder. I made PlaceHolder and I've no idea how to check that all textboxes have integer numbers as a text.

public void Made_Matrix (PlaceHolder Matrix, int Size){
for(int row=0; row < size; row++){
for(int col=0; col < size; col++){
TextBox TB = New TextBox();
Matrix.Controls.Add(TB);
TB.ID = TB + Convert.ToString(row) + Convert.ToString(col);
TB.AutoPostBack = "true";
}
Matrix.Controls.Add(new LiteralControl ("<br/>"));
}
}
public void TB_Validate (PlaceHolder Matrix, int Size){
for (int row = 0; row < size; row++){
for (int col = 0; col < size; col++){
string Ident = TB + Convert.ToString(row) + Convert.ToString(col);

how can i find text hidden in TextBox with ID from Ident? And how to check if it's numeric? I suppose that in .NET there's no function like IsNumeric(), am I right?