C# Program to write an array to a file

Writing an array to a file in C# can be accomplished using the File.WriteAllLines method from the System.IO namespace. This method writes each array element as a separate line to the specified file.

Syntax

Following is the syntax for using File.WriteAllLines −

File.WriteAllLines(string path, string[] contents);

Parameters

• path − The file path where the array will be written

• contents − The string array to write to the file

Using WriteAllLines Method

The WriteAllLines method automatically creates the file if it doesn't exist and overwrites it if it does. Each array element is written as a separate line in the file −

using System.IO;
using System;

public class Program {
   public static void Main() {
      string[] stringArray = new string[] {
         "one",
         "two",
         "three"
      };
      
      File.WriteAllLines("new.txt", stringArray);
      
      using (StreamReader sr = new StreamReader("new.txt")) {
         string res = sr.ReadToEnd();
         Console.WriteLine(res);
      }
   }
}

The output of the above code is −

one
two
three

Writing Different Array Types

For non-string arrays, you need to convert elements to strings first −

using System.IO;
using System;
using System.Linq;

public class Program {
   public static void Main() {
      int[] numbers = { 10, 20, 30, 40, 50 };
      
      // Convert int array to string array
      string[] stringNumbers = numbers.Select(x => x.ToString()).ToArray();
      
      File.WriteAllLines("numbers.txt", stringNumbers);
      
      // Read and display the file content
      string[] lines = File.ReadAllLines("numbers.txt");
      Console.WriteLine("File contents:");
      foreach (string line in lines) {
         Console.WriteLine(line);
      }
   }
}

The output of the above code is −

File contents:
10
20
30
40
50

Using WriteAllLines with File Path

You can specify a complete file path including directory −

using System.IO;
using System;

public class Program {
   public static void Main() {
      string[] fruits = { "Apple", "Banana", "Orange", "Mango" };
      string filePath = Path.Combine(Environment.CurrentDirectory, "fruits.txt");
      
      File.WriteAllLines(filePath, fruits);
      Console.WriteLine("Array written to: " + filePath);
      
      // Verify the file was created
      if (File.Exists(filePath)) {
         string[] readLines = File.ReadAllLines(filePath);
         Console.WriteLine("Total lines written: " + readLines.Length);
      }
   }
}

The output of the above code is −

Array written to: C:\path\to\current\directory\fruits.txt
Total lines written: 4

Comparison of File Writing Methods

Conclusion

The File.WriteAllLines method provides a simple and efficient way to write array contents to a file in C#. Each array element is automatically written as a separate line, making it ideal for storing lists of data that can be easily read back later.