Save and load a small text file

Your program ends. What could make a note appear again on the next run? Save a small file, then test the first run when it does not exist yet.

Variables disappear when this console program ends. A file can keep text for a later run. We will use one clearly named practice file, study-notes.txt, in a dedicated practice project folder. The name is relative to the process working directory, usually the folder from which you run the command. It is not automatically relative to Program.cs.

Predict a save-and-read round trip

Run this complete program from your practice folder. It writes two lines, reads the file into a string, then prints that string. Write the expected output before running. The backslash-n escape inside the string represents a line break.

using System;
using System.IO;

string path = "study-notes.txt";
try
{
    File.WriteAllText(path, "Read variables\nPractise loops");
    string notes = File.ReadAllText(path);
    Console.WriteLine(notes);
}
catch (UnauthorizedAccessException)
{
    Console.WriteLine("The notes location is not writable or readable.");
}
catch (IOException)
{
    Console.WriteLine("The notes could not be saved or read.");
}

program string
  "Read variables\nPractise loops"
            | WriteAllText
            v
      study-notes.txt
            | ReadAllText
            v
      notes string --> Console.WriteLine

WriteAllText creates the file when needed. If the target file already exists, it replaces its contents. Use the practice file for this exercise, and inspect it in your editor after running. Rerunning this same program writes the same two-line content again; it does not append another copy. ReadAllText reads the complete file, so it suits these small notes.

Your turn: load without creating a file

Write a loader that reads an existing study-notes.txt. On a first run with no file, it should print No saved notes yet. A missing file is a situation this loader deliberately handles. Compare your attempt with the complete solution below. To test the missing-file path, run it from a fresh practice folder with no study-notes.txt.

using System;
using System.IO;

string path = "study-notes.txt";
try
{
    string notes = File.ReadAllText(path);
    Console.WriteLine($"Saved notes: {notes}");
}
catch (FileNotFoundException)
{
    Console.WriteLine("No saved notes yet.");
}
catch (UnauthorizedAccessException)
{
    Console.WriteLine("The notes cannot be accessed at this location.");
}
catch (IOException)
{
    Console.WriteLine("The notes could not be read.");
}

With a file containing exactly Practise methods, expect Saved notes: Practise methods. With an empty file, expect Saved notes: followed by no note text. With no file, expect the missing-file message. Each case tells you something different about the stored state.

Both File helper methods open and close their file handles for this operation; no manual stream needs to be closed in these examples. The using System.IO; line imports a namespace; it is different from a resource-management using statement. You will meet streams when you need to process larger data gradually.

Explain it back

Explain where the relative path is resolved, what a second save does, and why a successful filename check cannot promise a later read will succeed. The catches report failure rather than pretending notes were loaded. Other failures can still surface when a program has no meaningful recovery; this is a small teaching example, not a complete storage system.

References: Microsoft - File.WriteAllText and File.ReadAllText.