calculation between two comboBox

Question

Hi All.

I have two combobox .I need to multiply comboBox1 and comboBox2 then the result in comboBox3.
somebody show me the code.Below the code what I try to do.

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

namespace Office_aa
{
    public partial class Form1 : Form
    {
        List<string> Quantity = new List<string>();
        List<string> Unit_Price = new List<string>();
        public Form1()
        {
            InitializeComponent();

            for (int i = 1; i < 100; i++)
                Quantity.Add(i.ToString());

            foreach (string item in Quantity)
            {
                comboBox1.Items.Add(item);
                comboBox4.Items.Add(item);
            }

            for (int i = 50; i < 500; i++)
                Unit_Price.Add(i.ToString("$#,##0.00"));

            foreach (string item in Unit_Price)
            {
                comboBox2.Items.Add(item);
                comboBox5.Items.Add(item);
            }
        }

        private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
        {

            var Amount = new List<double>();

            double Result = double.Parse(comboBox1.Text) * double.Parse(comboBox2.Text);
            Amount.Add(Result);

            foreach (var item in Amount)
            {
                comboBox3.Items.Add(item);
                comboBox6.Items.Add(item);
            }


        }
    }
}

Answer 1

@MiPakTeh , you could try the following code to get the result after you choose the value from combobox1 and combobox2.

 public partial class Form1 : Form  
    {  
        List<string> Quantity = new List<string>();  
        List<string> Unit_Price = new List<string>();  
  
        NumberStyles currencyStyle = NumberStyles.Currency;  
        NumberFormatInfo numberFormat = CultureInfo.CurrentCulture.NumberFormat;  
        public Form1()  
        {  
            InitializeComponent();  
            CultureInfo.CurrentCulture = new CultureInfo("en-US");  
  
            for (int i = 1; i < 100; i++)  
                Quantity.Add(i.ToString());  
  
            foreach (string item in Quantity)  
            {  
                comboBox1.Items.Add(item);  
                 
            }  
  
            for (int i = 50; i < 500; i++)  
                Unit_Price.Add(i.ToString("$#,##0.00"));  
  
            foreach (string item in Unit_Price)  
            {  
                comboBox2.Items.Add(item);  
         
            }  
        }  
        int firstvalue;  
        bool t;  
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)  
        {  
            if(int.TryParse(comboBox1.Text, out firstvalue))  
            {  
                t = true;  
            }  
           
        }  
  
        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)  
        {  
            if(double.TryParse(comboBox2.Text, currencyStyle, numberFormat, out var secondvalue)&&t)  
            {  
                double Result_ = firstvalue*secondvalue;  
                comboBox3.Items.Add(Result_.ToString("$#,##0.00"));  
            }  
        }  
    }  

Result:

---

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Answer 2

In your comboBox3_SelectedIndexChanged method you're parsing comboBox2.Text as a double but the Parse method needs to be told that the input string is an en-US-style currency string, or it'll end up throwing a FormatException, so you'd probably want to do something like this to parse comboBox2.Text:

Console.WriteLine(500000.ToString("$#,##0.00")); // $500,000.00
Console.WriteLine(double.Parse("$500,000.00", NumberStyles.Currency, new CultureInfo("en-US").NumberFormat)); // 500000.00

You'd also probably want to avoid calculating Result if either two values fail to parse, so something like this:

NumberStyles currencyStyle = NumberStyles.Currency;
NumberFormatInfo numberFormat = new CultureInfo("en-US").NumberFormat;

if (!int.TryParse(comboBox1.Text, out var value1) || !double.TryParse(comboBox2.Text, currencyStyle, numberFormat, out var value2))
    return;

double Result = value1 * value2;

If you'd rather not have to refer to a hard-coded new CultureInfo("en-US") every time you parse a date, you just need to make sure you're setting the current culture in your app on startup, then you can just pass in the current culture when you parse your amounts:

CultureInfo.CurrentCulture = new CultureInfo("en-US");

// ...

NumberStyles currencyStyle = NumberStyles.Currency;
NumberFormatInfo numberFormat = CultureInfo.CurrentCulture.NumberFormat;

if (!int.TryParse(comboBox1.Text, out var value1) || !double.TryParse(comboBox2.Text, currencyStyle, numberFormat, out var value2))
    return;

double Result = value1 * value2;

Answer 3

I don't have a solution but instead code that shows a better approach that there is no guessing of types. Note also I use SelectionChangeCommitted rather than SelectionChanged

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Windows.Forms;  
  
namespace CodeSample_1  
{  
    public partial class Form1 : Form  
    {  
        public Form1()  
        {  
            InitializeComponent();  
  
            Shown += OnShown;  
        }  
  
        private void OnShown(object sender, EventArgs e)  
        {  
            comboBox1.DataSource = Enumerable.Range(1, 100).ToList();  
            comboBox2.DataSource = Enumerable.Range(50, 500).ToList();  
  
            comboBox1.SelectionChangeCommitted += ComboBoxOnSelectionChangeCommitted;  
            comboBox2.SelectionChangeCommitted += ComboBoxOnSelectionChangeCommitted;  
            SelectionChange_C1_C2();  
  
            List<NumberItem> numberItems = new List<NumberItem>();  
            for (int index = 5; index < 10; index++)  
            {  
                numberItems.Add(new NumberItem()  
                {  
                    Display = index.ToString("$#,##0.00"),   
                    Value = index  
                });  
            }  
  
            comboBox3.DataSource = numberItems;  
            comboBox3.SelectionChangeCommitted += ComboBox3OnSelectionChangeCommitted;  
            Combo3Changed();  
  
        }  
  
        private void ComboBox3OnSelectionChangeCommitted(object sender, EventArgs e)  
        {  
            Combo3Changed();  
        }  
  
        private void Combo3Changed()  
        {  
            label3.Text = ((NumberItem)comboBox3.SelectedItem).Value.ToString();  
        }  
  
        private void ComboBoxOnSelectionChangeCommitted(object sender, EventArgs e)  
        {  
            SelectionChange_C1_C2();  
        }  
  
        private void SelectionChange_C1_C2()  
        {  
            var c1 = (int)comboBox1.SelectedItem;  
            var c2 = (int)comboBox2.SelectedItem;  
            label1.Text = $"Combo 1: {c1} Combo 2: {c2}";  
            var result = c1 * c2;  
            label2.Text = result.ToString();  
        }  
    }  
  
    public class NumberItem  
    {  
        public string Display { get; set; }  
        public int Value { get; set; }  
        public override string ToString() => Display;  
    }  
}  
  

Answer 4

Thank paul,
problem solve in calculate but 2 thing can't do.
1.when use event
private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
{

    }

this method cannot fire
2.Always caculate everytime push button_1

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

namespace Office_aa
{
    public partial class Form1 : Form
    {
        List<string> Quantity = new List<string>();
        List<string> Unit_Price = new List<string>();

        NumberStyles currencyStyle = NumberStyles.Currency;
        NumberFormatInfo numberFormat = CultureInfo.CurrentCulture.NumberFormat;

        public Form1()
        {
            InitializeComponent();

            CultureInfo.CurrentCulture = new CultureInfo("en-US");

            for (int i = 1; i < 100; i++)
                Quantity.Add(i.ToString());

            foreach (string item in Quantity)
            {
                comboBox1.Items.Add(item);
                comboBox4.Items.Add(item);
            }

            for (int i = 50; i < 500; i++)
                Unit_Price.Add(i.ToString("$#,##0.00"));

            foreach (string item in Unit_Price)
            {
                comboBox2.Items.Add(item);
                comboBox5.Items.Add(item);
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (!int.TryParse(comboBox1.Text, out var value1) || !double.TryParse(comboBox2.Text, currencyStyle, numberFormat, out var value2))
                return;
            double Result = value1 * value2;
            if (!int.TryParse(comboBox4.Text, out var value1_) || !double.TryParse(comboBox5.Text, currencyStyle, numberFormat, out var value2_))
                return;
            double Result_ = value1_ * value2_;

            comboBox3.Items.Add(Result);
            comboBox6.Items.Add(Result_);

        }

        private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
    }
}