/// <summary>
/// method : btnUpdate_Click
/// </summary>
/// <param name="sender">The sender.</param>
/// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
private void btnUpdate_Click(object sender, EventArgs e)
{
var calcLine = txtReplacementValue.Text;
var firstChar = calcLine[0];
if (firstChar == '+' || firstChar == '-')
{
var secondChar = calcLine[1];
if (char.IsDigit(secondChar))
{
var calc = new CalcLine(calcLine);
calculation.Replace(calc, lstCalculationLines.SelectedIndex);
}
else
{
MessageBox.Show("The characters immediately following the first character must be numeric", "Error");
}
}
else
{
MessageBox.Show("The first character must be a + or - ", "Error");
}
}