C# convert a long to string

Use the ToString() method like this:

textBox1.Text = CountLinesInFile("test.txt").ToString();

In Java its a simply .ToString

And in C#, its simply .ToString().

Happy learning.

just write

textBox1.Text =(CountLinesInFile("test.txt")).ToString(); 

MSDN: Object.ToString Method - Returns a string that represents the current object.