How to exit from a Function after execution

Question

How do i exit a function immediately, like i want this to check if goods are in-stock should the goods be in-stock it should allow to place order, if not it should show the Error message and then on clicking the OK button it returns to the solution without running another method / function.

My code looks like this :

private void CheckForInStockGoods()
{
    using (SqlConnection con = new SqlConnection(constring))
    {
        con.Open();
        string checkQuery = "select * from productsmarket_Table where productname like '" + product_search.Text + "%' ";
        using (SqlCommand cmd = new SqlCommand(checkQuery, con))
        {
            try
            {
                using (SqlDataReader rd = cmd.ExecuteReader())
                {
                    if (rd.Read())
                    {
                        int availableQty = Convert.ToInt32((rd["productQty"].ToString()));
                        if (availableQty == 0)
                        {
                            MessageBox.Show("You cannot Place This Order\n You appear to be out of stock!", "Out of Stock", MessageBoxButtons.OK, MessageBoxIcon.Error);
                            return;
                        }
                    }
                }
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }
    }
}

Edit Full source code looks like this :

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace NOLANPAY
{
    public partial class SalesUserEnd : Form
    {
        decimal SumValue = 0;
        string invoiceNumber = generateInvoiceNumber();
        int updateVolume;

        string constring = ConfigurationManager.ConnectionStrings["MyDBConnectionString"].ToString();
        public SalesUserEnd()
        {
            InitializeComponent();
        }

        private void Button2_Click(object sender, EventArgs e)
        {
            using (SqlConnection con = new SqlConnection(constring))
            {
                con.Open();
                string query = "select * from productsmarket_Table where productname like '"+product_search.Text+"%' ";
                using (SqlDataAdapter da = new SqlDataAdapter(query, con))
                {
                    try
                    {
                        DataTable dt = new DataTable();
                        da.Fill(dt);
                        dataGridView1.DataSource = dt;
                        con.Close();
                    }
                    catch(Exception ex)
                    {
                        MessageBox.Show(ex.ToString());
                    }
                }
            }
        }

        private void DataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            if (dataGridView1.SelectedRows.Count > 0)
            {
                string productName = dataGridView1.SelectedRows[0].Cells[1].Value + string.Empty;
                string price = dataGridView1.SelectedRows[0].Cells[3].Value + string.Empty;

                chprodName.Text = productName;
                price_2.Text = price;
            }
        }

        private void Button1_Click(object sender, EventArgs e)
        {
            CheckForInStockGoods();
            decimal netPrice = Convert.ToDecimal(prod_qty.Text) * Convert.ToDecimal(price_2.Text);
            string finalPrice = Convert.ToString(netPrice);
            string DateOfPurchase = System.DateTime.Now.ToString();

            string notify = "These items would be added to Tray, Please confirm?";
            DialogResult result = MessageBox.Show(notify, "Confirm", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
            if (result == DialogResult.Yes)
            {
                listView1.View = View.Details;
                ListViewItem lvItem = listView1.Items.Add(chprodName.Text);
                lvItem.SubItems.Add(price_2.Text);
                lvItem.SubItems.Add(prod_qty.Text);
                lvItem.SubItems.Add(finalPrice);
                lvItem.SubItems.Add(DateOfPurchase);
            }
        }

        private void CheckForInStockGoods()
        {
            using (SqlConnection con = new SqlConnection(constring))
            {
                con.Open();
                string checkQuery = "select * from productsmarket_Table where productname like '" + product_search.Text + "%' ";
                using (SqlCommand cmd = new SqlCommand(checkQuery, con))
                {
                    try
                    {
                        using (SqlDataReader rd = cmd.ExecuteReader())
                        {
                            if (rd.Read())
                            {
                                int availableQty = Convert.ToInt32((rd["productQty"].ToString()));
                                if (availableQty == 0)
                                {
                                    MessageBox.Show("You cannot Place This Order\n You appear to be out of stock!", "Out of Stock", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                    return;
                                }
                            }
                        }
                    }
                    catch(Exception ex)
                    {
                        MessageBox.Show(ex.ToString());
                    }
                }
            }
        }

        private void Button5_Click(object sender, EventArgs e)
        {

        }

        public static string generateInvoiceNumber()
        {
            string shopMasterPrologue = "#SHOPMAS1";
            Random rand = new Random();
            int randomLength = rand.Next(1, 6900);
            string FinalRandom = shopMasterPrologue + randomLength;
            return FinalRandom;
        }

        private void Button3_Click(object sender, EventArgs e)
        {
            decimal finalPrice = Convert.ToDecimal(excess.Text) - Convert.ToDecimal(totalPrice.Text);
            //decimal FinalBalance = Convert.ToDecimal(finalPrice); // Aww Snap, i dont need this sir!
            bal.Text = Convert.ToString(finalPrice);
            button3.Enabled = false;
            button3.Text = "Balance Calculated";
            string changeInfo = "Recieved by Sammi" + " For The Products: " + getAllboughtProds() + "With Excess Balace of : "+bal.Text + " And Excess Payment of "+ excess.Text + " On " + System.DateTime.Now;
            SaveTransactionRecord(invoiceNumber, changeInfo);
        }

        private void SalesUserEnd_Load(object sender, EventArgs e)
        {
            label9.Text = " ";
        }

        private void Button5_Click_1(object sender, EventArgs e)
        {
            foreach (ListViewItem lstItem in listView1.Items)
            {
                SumValue += decimal.Parse(lstItem.SubItems[3].Text);
                label9.Text = "Total : NGN "+ SumValue;
                totalPrice.Text = Convert.ToString(SumValue);
                button5.Enabled = false;
                button5.Text = "Calculated";
                excess.Text = "0.00";
                bal.Text = "0.00";

            }

            DialogResult res = MessageBox.Show("Price as at checkout is : " + SumValue + " Please Select Yes to Confirm Order", "Confirm", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
            if (res == DialogResult.Yes)
            {
                string info = "Recieved by Sammi" + " For The Products: "+ getAllboughtProds() + " On "+System.DateTime.Now;
                MessageBox.Show("Order Complete!");
                //Save for Transaction and generate 
                UpdateProductQuantity();
                SaveTransactionRecord(invoiceNumber,info);

            }
        }

        private void UpdateProductQuantity()
        {
            using (SqlConnection con = new SqlConnection(constring))
            {
                con.Open();
                //Starting calls.
                //Select all first to check for Quantity
                string updateQtyQuery = "select* from productsmarket_Table where productname like '"+product_search.Text+"%' ";
                using (SqlCommand cmd = new SqlCommand(updateQtyQuery, con))
                {
                    using (SqlDataReader rd = cmd.ExecuteReader())
                    {
                        if (rd.Read())
                        {
                            int orginalQty = Convert.ToInt32((rd["productQty"].ToString()));
                            updateVolume = orginalQty - Convert.ToInt32(prod_qty.Text);
                        }
                    }

                    string updateSqlQuantity = "update productsmarket_Table set productQty = @productQty where productname= @productname";
                    using (SqlCommand cmd2 = new SqlCommand(updateSqlQuantity, con))
                    {
                        try
                        {
                            cmd2.Parameters.AddWithValue("@productQty", updateVolume);
                            cmd2.Parameters.AddWithValue("@productname", product_search.Text);
                            cmd2.ExecuteNonQuery();

                            //Works Good!
                        }
                        catch(Exception ex)
                        {
                            MessageBox.Show(ex.ToString());
                        }
                    }
                }
            }
        }

        private void SaveTransactionRecord(string invoiceNumber,string data)
        {
            using (SqlConnection con = new SqlConnection(constring))
            {
                con.Open();
                string saveQuery = "insert into salesTransactionTable (invoiceNumber,data,transactionDate) values (@invoiceNumber,@data,@transactionDate)";
                using (SqlCommand cmd = new SqlCommand(saveQuery,con))
                {
                    try
                    {
                        cmd.Parameters.AddWithValue("@invoiceNumber",invoiceNumber);
                        cmd.Parameters.AddWithValue("@data", data);
                        cmd.Parameters.AddWithValue("@transactionDate", System.DateTime.Now);
                        cmd.ExecuteNonQuery();

                    }
                    catch(Exception ex)
                    {
                        MessageBox.Show(ex.ToString());
                    }
                }
            }
        }

        private string getAllboughtProds()
        {
            string allBoughtItems = null;
            foreach (ListViewItem lstItem in listView1.Items)
            {
                allBoughtItems += lstItem.SubItems[0].Text + ",";
            }
            return allBoughtItems;
        }

        private void Button4_Click(object sender, EventArgs e)
        {

            if (printPreviewDialog1.ShowDialog() == DialogResult.OK)
            {
                printDocument1.Print();
            }
        }

        private void PrintDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
        {
            int x = 100, y = 100;
            /*Image newImage = Properties.Resources.logo;
            int width = 150, height = 70;
            int ix = x, iy = y; //image position
            e.Graphics.DrawImage(newImage, ix, iy, width, height);*/
            var header = new Font("Calibri", 21, FontStyle.Bold);
            int hdy = (int)header.GetHeight(e.Graphics); //30; //line height spacing

            var fnt = new Font("Courier New", 10, FontStyle.Bold);
            int dy = (int)fnt.GetHeight(e.Graphics); //20; //line height spacing

            e.Graphics.DrawString("Receipt", header, Brushes.Black, new PointF(x, y)); y += hdy;
            e.Graphics.DrawString("Invoice #: " + invoiceNumber, fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("-----------------------------------------------------------", fnt, Brushes.Black, new PointF(x, y)); y += dy;

            e.Graphics.DrawString(" Product Name  "+"   |  "+" Price " + "   |  "+" Qty" +"   |  "+ " Net Price " , fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("-----------------------------------------------------------", fnt, Brushes.Black, new PointF(x, y)); y += dy;

            for (int i = 0; i < listView1.Items.Count; i++)
            {
                // Draw the row details for ? receipt 
                e.Graphics.DrawString(" " + listView1.Items[i].SubItems[0].Text +"   |  " + listView1.Items[i].SubItems[1].Text +"  |   "+
                  listView1.Items[i].SubItems[2].Text + "    | "+ listView1.Items[i].SubItems[3].Text, fnt, Brushes.Black, new PointF(x, y)); y += dy;
            }
            e.Graphics.DrawString("---------------------", fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("Total : " + totalPrice.Text, fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("Excess : " + excess.Text, fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("Balance : " + bal.Text, fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("------------------------------------------------------", fnt, Brushes.Black, new PointF(x, y)); y += dy;
            e.Graphics.DrawString("Thank you for your Patronage ", fnt, Brushes.Black, new PointF(x, y)); y += dy;
        }
    }
}

Answer 1

The return statement allows you to exit a method/function, thus leaving the scope.

Sorry for the late edit/addition.

Using the return statement is only mandatory when leaving a method which returns a value, or when leaving a method early.

I'll give you an example:

public void Foo() {
    // No return value
    if (myCondition == expectedValue) {
        // Do something with data
    } else {
        // myCondition has an unexpected value; ABORT
        return; // Leave early
    }
    // Do more stuff (this could also be shortened)
}

public int Bar() {

    if (myCondition == badValue) {
        return myErrorCode; // We're exiting the method early with an error code
        // You could also do this w/ exceptions
    }
    // No need for else
    DoStuffWData(myData);

    // Some condition where the data is returned, and not zero
    if (myData == ushort.MaxValue) {
        return myData;
    }

    return 0; // Mandatory return; the method returns a value.
}

Answer 2

You should consider modifying the return type of CheckForInStockGoods method to bool and return false if availableQty == 0 instead of simply return. In usual case, return true.

Then change a bit of the logic in the Button1_Click method. Do something like this:

if(CheckForInStockGoods())
{
    // your usual piece of logic to run if the goods are in stock.
}