format code in md

solutions/compound-types/slice.md

@@ -1,4 +1,5 @@
 1.
+
 ```rust
 fn main() {
     let arr = [1, 2, 3];
@@ -9,18 +10,20 @@ fn main() {
 ```
 
 2.
+
 ```rust
 fn main() {
     let arr: [char; 3] = ['中', '国', '人'];
 
     let slice = &arr[..2];
-    
+
     // TIPS: slice( reference ) IS NOT an array, if it is an array, then `assert!` will passed: each of the two UTF-8 chars '中' and '国'  occupies 3 bytes, 2 * 3 = 6
     assert!(std::mem::size_of_val(&slice) == 16);
 }
 ```
 
 3.
+
 ```rust
 fn main() {
     let arr: [i32; 5] = [1, 2, 3, 4, 5];
@@ -30,6 +33,7 @@ fn main() {
 ```
 
 4.
+
 ```rust
 fn main() {
     let s = String::from("hello");
@@ -42,6 +46,7 @@ fn main() {
 ```
 
 5.
+
 ```rust
 fn main() {
     let s = "你好，世界";
@@ -52,6 +57,7 @@ fn main() {
 ```
 
 6.
+
 ```rust
 fn main() {
     let mut s = String::from("hello world");
@@ -63,8 +69,8 @@ fn main() {
     println!("the first word is: {}", word);
 
     s.clear();
-
 }
+
 fn first_word(s: &str) -> &str {
     &s[..1]
 }