//The following line is put ahead of all the below code: private decimal decSubTotal = 0M; private void calculateButton_Click(object sender, EventArgs e) { string strMessageString; //Calculate the cost of the vehicle. if (this.basePriceMaskedTextBox.Text != "") { //Convert from Text to Decimal value. ** decSubTotal = decimal.Parse(this.basePriceMaskedTextBox.Text); if (this.tradeInAllowanceMaskedTextBox.Text != "") { decTradeInAllowance = ** decimal.Parse(this.tradeInAllowanceMaskedTextBox.Text); decSubTotal += decTradeInAllowance; this.subTotalLabel.Text = decSubTotal.ToString("C"); } } }