Add variables and types tutorial for Scala

tutorials/learnscala.org/en/Variables and Types.md

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+Tutorial
+--------
+
+Scala is statically typed, so variable types are known at compile time. However, Scala also supports type inference in variable declaration.
+
+The basic types in Scala are:
+
+* `Byte`
+* `Short`
+* `Int`
+* `Long`
+* `Float`
+* `Double`
+* `Char`
+* `String`
+* `Boolean`
+
+### Numbers
+
+To declare and assign a number in Scala, you can use the following syntax:
+
+    val myNumber: Int = 5
+
+You can also use type inference:
+
+    val myNumber = 5
+
+For floating-point numbers an 'f' suffix is needed to specify that it is a float:
+
+    val d: Double = 4.5
+    val f: Float = 4.5f
+
+### Characters
+
+A character is defined using single quotes:
+
+    val c: Char = 'g'
+
+### Strings
+
+A string is defined using double quotes:
+
+    val s: String = "Hello, world!"
+
+### Booleans
+
+A boolean is defined as either `true` or `false`:
+
+    val b: Boolean = true
+
+### Val and Var
+
+Variables in Scala are either declared using `val` or `var`.
+
+Any variables declared using `val` are immutable and cannot be changed once assigned, but variables declared with `var` are mutable and can be changed after assignment.
+
+In this case, the value of `pi` will not change, so we should declare it using `val`:
+
+    val pi: Double = 3.14159
+
+While in this case, the value of `counter` may change, so we should declare it with `var`:
+
+    var counter: Int = 0
+
+
+Exercise
+--------
+
+Define variables with the following values:
+
+A string named `productName` equal to "Laptop".
+An integer named `productYear` equal to 2023.
+A double named `productPrice` equal to 999.99.
+
+
+Tutorial Code
+-------------
+    object Main {
+        def main(args: Array[String]): Unit = {
+            // Define variables here
+
+            // Test code
+            println("productName: " + productName)
+            println("productYear: " + productYear)
+            println("productPrice: " + productPrice)
+        }
+    }
+Expected Output
+---------------
+productName: Laptop
+productYear: 2023
+productPrice: 999.99
+
+Solution
+--------
+    object Main {
+        def main(args: Array[String]): Unit = {
+            val productName: String = "Laptop"
+            val productYear: Int = 2023
+            val productPrice: Double = 999.99
+
+            // Test code
+            println("productName: " + productName)
+            println("productYear: " + productYear)
+            println("productPrice: " + productPrice)
+        }
+    }