fix code

Author: k-nasa

chapter3/src/3_9_2/main.rs

@@ -1,9 +1,11 @@
+use rand::Rng;
 use std::fs::File;
 use std::io;
 use std::io::Write;
 
 fn main() -> io::Result<()> {
-    let bytes = rand::thread_rng().gen::<[u8; 1024]>();
+    let mut bytes = [0u8; 1024];
+    rand::thread_rng().fill(&mut bytes);
 
     let mut file = File::create("random.txt")?;
     file.write_all(&bytes)?;

chapter3/src/3_9_5/main.rs

@@ -20,7 +20,10 @@ where
 }
 
 fn main() -> Result<()> {
-    let mut file = File::open("test.txt").expect(r#"動作には4バイト以上の "{}/test.txt" が必要です。"#, std::env::current_dir()?.display());
+    let mut file = File::open("test.txt").expect(&format!(
+        "動作には4バイト以上の {}/test.txt が必要です",
+        std::env::current_dir()?.display()
+    ));
     let mut new_file = File::create("new_test.txt")?;
 
     copy_n(&mut file, &mut new_file, 4)?;