Each data type (int, float, bool, etc.) has a TryParse method attempts to parse a string and returns true if it is successful. You can use this to determine whether a textbox contains a valid value.

The following code shows how the program determines whether the value entered in the first textbox contains a valid integer.

// See if the text is an int.
private void txtInteger_TextChanged(object sender, EventArgs e)
{
    int value;
    if (int.TryParse(txtInteger.Text, out value))
    {
        txtInteger.BackColor = Color.White;
    }
    else
    {
        txtInteger.BackColor = Color.Yellow;
    }
}

The code declares the variable value. It then calls TryParse to attempt to parse the text in txtInteger. The code gives the textbox a white or yellow background depending on whether TryParse returns true or false.

The event handlers for the other textboxes are similar. They just use other data types instead of int.