Hello i need help fixing my C# code as its giving me the error Possible unintended reference comparison; to get a value comparison, cast the left hand side to type 'string'

the code:

using System;

using System.Collections.Generic;

using System.Data;

using System.Text;

using System.Threading.Tasks;

using System.Drawing;

using System.ComponentModel;

using System.Linq;

using System.Windows.Forms;

namespace PizzaMiniProject {

public partial class ApplicationForm1 : Form {

public ApplicationForm1() {

InitializeComponent();

}

private void btnAdd_Click(object sender, EventArgs e) {

bool error = false;

if (lbPizzaSelection.SelectedItem != null) {

if (txtQuantity.Text != "") {

lbQuantity.Items.Add(txtQuantity.Text);

int cost = 0;

if (lbPizzaSelection.SelectedItem == "Neapolitan") {

cost = Convert.ToInt32(txtQuantity.Text) * 50;

lbAmount.Items.Add(cost);

}

if (lbPizzaSelection.SelectedItem == "Margherita") {

cost = Convert.ToInt32(txtQuantity.Text) * 60;

lbAmount.Items.Add(cost);

}

if (lbPizzaSelection.SelectedItem == "Pepperoni") {

cost = Convert.ToInt32(txtQuantity.Text) * 80;

lbAmount.Items.Add(cost);

}

if (lbPizzaSelection.SelectedItem == "Lazio") {

cost = Convert.ToInt32(txtQuantity.Text) * 70;

lbAmount.Items.Add(cost);

}

if (lbPizzaSelection.SelectedItem == "Zucchini") {

cost = Convert.ToInt32(txtQuantity.Text) * 90;

lbAmount.Items.Add(cost);

}

txtQuantity.Focus();

txtQuantity.Clear();

} else {

error = true;

MessageBox.Show("Please enter a valid Quantity", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

lblAmount.Focus();

}

if (error == false) {

lbOrdered.Items.Add(lbPizzaSelection.SelectedItem);

lbPizzaSelection.Items.Remove(lbPizzaSelection.SelectedItem);

}

} else {

MessageBox.Show("No Pizza Selected", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

}

}

private void txtQuantity_KeyPress(object sender, KeyPressEventArgs e) {

char ch = e.KeyChar;

if (!Char.IsDigit(ch) && ch != 8) //method makes it so all digits[numbers] can be clicked expect the backwards which is 8.

{

e.Handled = true;

MessageBox.Show("Quantity must be a number!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

}

}

private void BtnReset_Click(object sender, EventArgs e) {

if (checkDelivery.Checked) {

checkDelivery.Checked = false;

}

lbOrdered.Items.Clear();

lbAmount.Items.Clear();

lbQuantity.Items.Clear();

lbPizzaSelection.Items.Clear();

lblAmount.Text = "";

lblOrder.Text = "";

MessageBox.Show("Form Reset.", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);

}

private void btnOrder_Click(object sender, EventArgs e) {

if (lbOrdered.Items.Count > 0) {

int sum = 0;

for (int i = 0; i < lbAmount.Items.Count; i++) {//using a dummy variable i to store

sum += Convert.ToInt32(lbAmount.Items[i].ToString());//convert to int or double in order to be mathimtical

}//add to the sum instead of keeps changing in order to get total value.

lblAmount.Text = Convert.ToString(sum);//once done re-convert to string t be used.

double[] currencies = { 1, 3.67, 5.12 };

int currency = 0;

if (currencyUAE.Checked) {

currency = 0;

}

if (currencyUS.Checked) {

currency = 1;

}

if (currencyEuro.Checked) {

currency = 2;

}

double price = int.Parse(lblAmount.Text) / currencies[currency];

lblAmount.Text = string.Format("{0:#.##}", price);

if (checkDelivery.Checked) {

double totalPrice = double.Parse(lblAmount.Text) + (double.Parse(lblAmount.Text) * 0.05);

lblOrder.Text = string.Format("{0:#.##}", totalPrice);

MessageBox.Show("Have a nice meal! - No Express Delivery!");

} else {

double totalPrice = double.Parse(lblAmount.Text);

lblOrder.Text = string.Format("{0:#.##}", totalPrice);

MessageBox.Show("Have a nice meal!");

}

} else {

MessageBox.Show("Place an order first!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

}

}

}

}