How to Read text file and Sort list in C#

You can use File.ReadAllLines or File.ReadLines to read the text file and store its contents into a list or array. After reading the file, you can sort the list using List<T>.Sort() method.

How to Read text file and Sort list in C#?

Open Visual Studio, then click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "ReadTextFileAndSort" and then click OK

Drag and drop the Button, and ListBox controls from the Visual Toolbox onto your form designer, then design your form as shown below.

The method btnOpen_Click is an event handler for a button click event in a Windows Forms application. When the user clicks the button (presumably labeled "Open"), the btnOpen_Click method is invoked.

private void btnOpen_Click(object sender, EventArgs e)
{
    using (OpenFileDialog ofd = new OpenFileDialog() { Filter = "Text Documents(*.txt)|*.txt", ValidateNames = true, Multiselect = false })
    {
        if (ofd.ShowDialog() == DialogResult.OK)
        {
            //Read text file
            string[] lines = System.IO.File.ReadAllLines(ofd.FileName);
            List<int> list = new List<int>();
            foreach (string s in lines)
            {
                list.Add(Convert.ToInt32(s));
                listReadFile.Items.Add(s);
            }
            //Sort list
            list.Sort();
            foreach (int x in list)
                listSort.Items.Add(x);
        }
    }
}

The ShowDialog() method opens the dialog and waits for the user to choose a file. If the user clicks OK, the method proceeds with reading and processing the file.

Once a file is selected, the method uses System.IO.File.ReadAllLines(ofd.FileName) to read the entire text file into a string array. Each line in the file becomes an individual element in the array.

The next step is to parse the contents of the text file. The method loops through each line, converts it to an integer, and adds it to a List<int>. This is done using Convert.ToInt32(s) to ensure the values are treated as integers.

After populating the list, the method sorts the List<int> in ascending order using the Sort() method.

Finally, the method loops through the sorted list and adds each item to another ListBox named listSort.

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