add solutions for variables

src/compound-types/array.md

@@ -87,3 +87,4 @@ fn main() {
 
 ```
 
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it

src/compound-types/enum.md

@@ -70,7 +70,7 @@ fn main() {
 } 
 ```
 
-🌟🌟 使用枚举对类型进行同一化
+🌟🌟 
 
 ```rust,editable
 
@@ -198,4 +198,6 @@ fn main() {
     println!("linked list has length: {}", list.len());
     println!("{}", list.stringify());
 }
-```
+```
+
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it

src/compound-types/slice.md

@@ -86,3 +86,5 @@ fn first_word(s: &str) -> &str {
     &s[..1]
 }
 ```
+
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it

src/compound-types/string.md

@@ -251,5 +251,4 @@ fn main() {
 }
 ```
 
-
-
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it

src/compound-types/struct.md

@@ -213,4 +213,6 @@ fn main() {
 
     println!("{}, {}, {:?}",f.name, f.data, f);
 } 
-```
+```
+
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it

src/compound-types/tuple.md

@@ -75,3 +75,5 @@ fn sum_multiply(nums: (i32, i32)) -> (i32, i32) {
     (nums.0 + nums.1, nums.0 * nums.1)
 }
 ```
+
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it