diff --git a/src/exercise.rs b/src/exercise.rs
index 136e9439..e841aed2 100644
--- a/src/exercise.rs
+++ b/src/exercise.rs
@@ -3,7 +3,7 @@ use std::fmt::{self, Display, Formatter};
 use std::fs::{self, remove_file, File};
 use std::io::{self, BufRead, BufReader};
 use std::path::PathBuf;
-use std::process::{self, Command};
+use std::process::{self, exit, Command};
 use std::{array, env, mem};
 use winnow::ascii::{space0, Caseless};
 use winnow::combinator::opt;
@@ -15,7 +15,8 @@ const RUSTC_NO_DEBUG_ARGS: &[&str] = &["-C", "strip=debuginfo"];
 const CONTEXT: usize = 2;
 const CLIPPY_CARGO_TOML_PATH: &str = "./exercises/22_clippy/Cargo.toml";
 
-fn not_done(input: &str) -> bool {
+// Checks if the line contains the "I AM NOT DONE" comment.
+fn contains_not_done_comment(input: &str) -> bool {
     (
         space0::<_, ()>,
         "//",
@@ -219,12 +220,15 @@ path = "{}.rs""#,
 
     pub fn state(&self) -> State {
         let source_file = File::open(&self.path).unwrap_or_else(|e| {
-            panic!(
-                "We were unable to open the exercise file {}! {e}",
-                self.path.display()
-            )
+            println!(
+                "Failed to open the exercise file {}: {e}",
+                self.path.display(),
+            );
+            exit(1);
         });
         let mut source_reader = BufReader::new(source_file);
+
+        // Read the next line into `buf` without the newline at the end.
         let mut read_line = |buf: &mut String| -> io::Result<_> {
             let n = source_reader.read_line(buf)?;
             if buf.ends_with('\n') {
@@ -236,70 +240,72 @@ path = "{}.rs""#,
             Ok(n)
         };
 
-        let mut matched_line_ind: usize = 0;
+        let mut current_line_number: usize = 1;
         let mut prev_lines: [_; CONTEXT] = array::from_fn(|_| String::with_capacity(256));
         let mut line = String::with_capacity(256);
 
         loop {
-            match read_line(&mut line) {
-                Ok(0) => break,
-                Ok(_) => {
-                    if not_done(&line) {
-                        let mut context = Vec::with_capacity(2 * CONTEXT + 1);
-                        for (ind, prev_line) in prev_lines
-                            .into_iter()
-                            .rev()
-                            .take(matched_line_ind)
-                            .enumerate()
-                        {
-                            context.push(ContextLine {
-                                line: prev_line,
-                                // TODO
-                                number: matched_line_ind - CONTEXT + ind + 1,
-                                important: false,
-                            });
-                        }
+            let n = read_line(&mut line).unwrap_or_else(|e| {
+                println!(
+                    "Failed to read the exercise file {}: {e}",
+                    self.path.display(),
+                );
+                exit(1);
+            });
 
-                        context.push(ContextLine {
-                            line,
-                            number: matched_line_ind + 1,
-                            important: true,
-                        });
-
-                        for ind in 0..CONTEXT {
-                            let mut next_line = String::with_capacity(256);
-                            let Ok(n) = read_line(&mut next_line) else {
-                                break;
-                            };
-
-                            if n == 0 {
-                                break;
-                            }
-
-                            context.push(ContextLine {
-                                line: next_line,
-                                number: matched_line_ind + ind + 2,
-                                important: false,
-                            });
-                        }
-
-                        return State::Pending(context);
-                    }
-
-                    matched_line_ind += 1;
-                    for prev_line in &mut prev_lines {
-                        mem::swap(&mut line, prev_line);
-                    }
-                    line.clear();
-                }
-                Err(e) => panic!(
-                    "We were unable to read the exercise file {}! {e}",
-                    self.path.display()
-                ),
+            // Reached the end of the file and didn't find the comment.
+            if n == 0 {
+                return State::Done;
             }
-        }
 
-        State::Done
+            if contains_not_done_comment(&line) {
+                let mut context = Vec::with_capacity(2 * CONTEXT + 1);
+                for (ind, prev_line) in prev_lines
+                    .into_iter()
+                    .take(current_line_number - 1)
+                    .enumerate()
+                    .rev()
+                {
+                    context.push(ContextLine {
+                        line: prev_line,
+                        number: current_line_number - 1 - ind,
+                        important: false,
+                    });
+                }
+
+                context.push(ContextLine {
+                    line,
+                    number: current_line_number,
+                    important: true,
+                });
+
+                for ind in 0..CONTEXT {
+                    let mut next_line = String::with_capacity(256);
+                    let Ok(n) = read_line(&mut next_line) else {
+                        break;
+                    };
+
+                    if n == 0 {
+                        break;
+                    }
+
+                    context.push(ContextLine {
+                        line: next_line,
+                        number: current_line_number + 1 + ind,
+                        important: false,
+                    });
+                }
+
+                return State::Pending(context);
+            }
+
+            current_line_number += 1;
+            // Recycle the buffers.
+            for prev_line in &mut prev_lines {
+                mem::swap(&mut line, prev_line);
+            }
+            line.clear();
+        }
     }
 
     // Check that the exercise looks to be solved using self.state()
@@ -428,17 +434,17 @@ mod test {
 
     #[test]
     fn test_not_done() {
-        assert!(not_done("// I AM NOT DONE"));
-        assert!(not_done("/// I AM NOT DONE"));
-        assert!(not_done("//  I AM NOT DONE"));
-        assert!(not_done("///  I AM NOT DONE"));
-        assert!(not_done("// I AM NOT DONE "));
-        assert!(not_done("// I AM NOT DONE!"));
-        assert!(not_done("// I am not done"));
-        assert!(not_done("// i am NOT done"));
+        assert!(contains_not_done_comment("// I AM NOT DONE"));
+        assert!(contains_not_done_comment("/// I AM NOT DONE"));
+        assert!(contains_not_done_comment("//  I AM NOT DONE"));
+        assert!(contains_not_done_comment("///  I AM NOT DONE"));
+        assert!(contains_not_done_comment("// I AM NOT DONE "));
+        assert!(contains_not_done_comment("// I AM NOT DONE!"));
+        assert!(contains_not_done_comment("// I am not done"));
+        assert!(contains_not_done_comment("// i am NOT done"));
 
-        assert!(!not_done("I AM NOT DONE"));
-        assert!(!not_done("// NOT DONE"));
-        assert!(!not_done("DONE"));
+        assert!(!contains_not_done_comment("I AM NOT DONE"));
+        assert!(!contains_not_done_comment("// NOT DONE"));
+        assert!(!contains_not_done_comment("DONE"));
     }
 }