add solutions for variables

src/basic-types/char-bool-unit.md

@@ -87,4 +87,6 @@ fn main() {
     let unit: () = ();
     assert!(size_of_val(&unit) == 4);
 }
-```
+```
+
+> 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/basic-types/functions.md

@@ -40,4 +40,6 @@ fn never_return() -> ! {
     // implement this function, don't modify fn signatures
     
 }
-```
+```
+
+> 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/basic-types/numbers.md

@@ -163,3 +163,5 @@ fn main() {
     println!("0x80 >> 2 is 0x{:x}", 0x80u32 >> 2);
 }
 ```
+
+> 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/basic-types/statements-expressions.md

@@ -56,4 +56,6 @@ fn main() {}
 fn sum(x: i32, y: i32) -> i32 {
     x + y;
 }
-```
+```
+
+> 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/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

src/flow-control.md

@@ -242,4 +242,6 @@ fn main() {
 
     assert!(count == __)
 }
-```
+```
+
+> 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/ownership/borrowing.md

@@ -163,4 +163,6 @@ fn main() {
     // add one line below to make a compiler error: cannot borrow `s` as mutable more than once at a time
     // you can't use r1 and r2 at the same time
 }
-```
+```
+
+> 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/ownership/ownership.md

@@ -161,3 +161,6 @@ fn main() {
    println!("{:?}, {:?}, {:?}", s1, s2, t);
 }
 ```
+
+
+> 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/pattern-match/match-iflet.md

@@ -193,3 +193,6 @@ 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/pattern-match/patterns.md

@@ -95,4 +95,6 @@ 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/variables.md

@@ -143,4 +143,7 @@ fn main() {
     // fill the blank to make the code work
     assert_eq!([x,y], __);
 } 
-```
+```
+
+
+> 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