In the text box (TextBox), only numbers and decimal places are allowed. -- (reference: column of zyg19800719)

// KeyPress event: when the control gets the focus and the user presses and releases the key on the keyboard
Private void textBox1_KeyPress (object sender, KeyPressEventArgs e) // the text box only accepts numbers and decimal places
{
// IsNumber: Specifies whether the character at the specified position in the string belongs to the digit category.
// IsPunctuation: Specifies whether the character at the specified position in the string belongs to the punctuation category.
// IsControl: Specifies whether the character at the specified position in the string belongs to the control character category.
If (! Char. IsNumber (e. KeyChar )&&! Char. IsPunctuation (e. KeyChar )&&! Char. IsControl (e. KeyChar ))
{
E. Handled = true; // gets or sets a value to indicate whether the System. Windows. Forms. Control. KeyPress event has been processed.
}
Else if (Char. IsPunctuation (e. KeyChar ))
{
If (e. KeyChar = '.')
{
If (TextBox) sender). Text. LastIndexOf ('.')! =-1)
{
E. Handled = true;
}
}
Else
{
E. Handled = true;
}
}
}