add variable exercises

en/src/variables.md

@@ -1 +1,119 @@
 # Variables
+
+### Binding and mutablity
+🌟 fix the error below with least change
+```rust,editable
+
+fn main() {
+    let x: i32; // uninitialized but using, ERROR !
+    let y: i32; // uninitialized but also unusing, only warning
+    println!("{} is equal to 5", x); 
+}
+```
+
+🌟🌟 fill the blanks in code to make it compile
+```rust,editable
+
+fn main() {
+    // replace __ with a variable name
+    let __ =  1;
+    __ += 2; 
+    
+    println!("{} is equal to 3", x); 
+}
+```
+
+### Scope
+🌟 fix the error below with least change
+```rust,editable
+
+fn main() {
+    let x: i32 = 10;
+    {
+        let y: i32 = 5;
+        println!("The value of x is {} and value of y is {}", x, y);
+    }
+    println!("The value of x is {} and value of y is {}", x, y); 
+}
+```
+
+🌟🌟 fix the error with the knowledge you grasped
+```rust,editable
+
+fn main() {
+    println!("{}, world", x); 
+}
+
+fn define_x() {
+    let x = "hello";
+}
+```
+
+### Shadowing
+🌟🌟 only change `assert_eq!` to make the `println!` work(print `42` in terminal)
+
+```rust,editable
+
+fn main() {
+    let x: i32 = 5;
+    {
+        let x = 12;
+        assert_eq!(x, 5);
+    }
+
+    assert_eq!(x, 12);
+
+    let x =  42;
+    println!("{}", x); // Prints "42".
+}
+```
+
+🌟🌟 remove a line in code to make it compile
+```rust,editable
+
+fn main() {
+    let mut x: i32 = 1;
+    x = 7;
+    // shadowing and re-binding
+    let x = x; 
+    x += 3;
+
+
+    let y = 4;
+    // shadowing
+    let y = "I can also be bound to text!"; 
+}
+```
+
+### Unused varibles
+fix the warning below with :
+
+- 🌟  one way
+- 🌟🌟  two ways
+
+> Note: there are two ways you can use, but none of them is removing the line `let x = 1` 
+
+```rust,editable
+
+fn main() {
+    let x = 1; 
+}
+
+// warning: unused variable: `x`
+```
+
+### Destructing
+🌟🌟 fix the error below with least change
+
+> Tips: you can use Shadowing or Mutability
+
+```rust,editable
+
+fn main() {
+    let (x, y) = (1, 2);
+    x += 2;
+
+    assert_eq!(x, 3);
+    assert_eq!(y, 2);
+}
+```