add solutions for basic-types, fix errors

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

@@ -1,7 +1,7 @@
 # Char, Bool and Unit
 
 ### Char
-🌟
+1. 🌟
 ```rust, editable
 
 // make it work
@@ -15,7 +15,7 @@ fn main() {
 } 
 ```
 
-🌟
+2. 🌟
 ```rust, editable
 
 // make it work
@@ -30,7 +30,7 @@ fn print_char(c : char) {
 ```
 
 ### Bool
-🌟
+3. 🌟
 ```rust, editable
 
 // make the println! work
@@ -44,7 +44,7 @@ fn main() {
 } 
 ```
 
-🌟
+4. 🌟
 ```rust, editable
 
 // make it work
@@ -57,7 +57,7 @@ fn main() {
 
 
 ### Unit type
-🌟🌟
+5. 🌟🌟
 ```rust,editable
 
 // make it work, don't modify `implicitly_ret_unit` !
@@ -78,7 +78,7 @@ fn explicitly_ret_unit() -> () {
 }
 ```
 
-🌟🌟 what's the size of the unit type?
+6. 🌟🌟 what's the size of the unit type?
 ```rust,editable
 
 // modify `4` in assert to make it work

src/basic-types/functions.md

@@ -1,11 +1,11 @@
 # Functions
-🌟🌟🌟
+1. 🌟🌟🌟
 ```rust,editable
 
 fn main() {
     // don't modify the following two lines!
     let (x, y) = (1, 2);
-    let s = sum(1, 2);
+    let s = sum(x, y);
 
     assert_eq!(s, 3);
 }
@@ -16,7 +16,7 @@ fn sum(x, y: i32) {
 ```
 
 
-🌟🌟
+2. 🌟
 ```rust,editable
 fn main() {
    print();
@@ -29,15 +29,16 @@ fn print() -> i32 {
 ```
 
 
-🌟🌟
+3. 🌟🌟🌟
 
 ```rust,editable
+// solve it in two ways
 fn main() {
     never_return();
 }
 
 fn never_return() -> ! {
-    // implement this function, don't modify fn signatures
+    // implement this function, don't modify the fn signatures
     
 }
 ```

src/basic-types/statements-expressions.md

@@ -25,9 +25,9 @@ fn main() {
 ```
 
 ### Exercises
-🌟🌟
+1. 🌟🌟
 ```rust,editable
-// make it work with two ways: both modify the inner {}
+// make it work with two ways
 fn main() {
    let v = {
        let mut x = 1;
@@ -38,7 +38,7 @@ fn main() {
 }
 ```
 
-🌟
+2. 🌟
 ```rust,editable
 
 fn main() {
@@ -48,10 +48,13 @@ fn main() {
 }
 ```
 
-🌟
+3. 🌟
 ```rust,editable
 
-fn main() {}
+fn main() {
+    let s = sum(1 , 2);
+    assert_eq!(s, 3);
+}
 
 fn sum(x: i32, y: i32) -> i32 {
     x + y;