add: arrays

14-arrays/01-whats-an-array/main.go

@@ -14,19 +14,89 @@ func main() {
 		myAge  byte
 		herAge byte
 
-		// uncomment the code below and observe the error
-		// wrongDeclaration [-1]byte
+		// this declares an array with two byte elements
+		// its length      : 2
+		// its element type: byte
+		ages [2]byte
 
-		zero    [0]byte
-		ages    [2]byte
+		// this declares an array with five string elements
+		// its length      : 5
+		// its element type: string
+		tags [5]string
+
+		// this array doesn't occupy any memory space (its length is zero)
+		// its length      : 0
+		// its element type: byte
+		zero [0]byte
+
+		// this array uses a constant expression
+		// its length      : 3
+		// its element type: byte
 		agesExp [2 + 1]byte
 
-		tags [5]string
+		// uncomment the code below and observe the error
+		//
+		// wrongDeclaration [-1]byte
 	)
 
-	fmt.Printf("%d %d\n", myAge, herAge)
-	fmt.Printf("%#v\n", zero)
-	fmt.Printf("%#v\n", ages)
-	fmt.Printf("%#v\n", agesExp)
-	fmt.Printf("%#v\n", tags)
+	fmt.Printf("myAge             : %d\n", myAge)
+	fmt.Printf("herAge            : %d\n", herAge)
+
+	// Since arrays we've declared here don't have any elements,
+	// Go automatically sets all their elements to their zero values
+	// depending on their element type.
+
+	// #v verb prints the array's length, element type and its elements
+	fmt.Printf("ages              : %#v\n", ages)
+	fmt.Printf("tags              : %#v\n", tags)
+	fmt.Printf("zero              : %#v\n", zero)
+	fmt.Printf("agesExp           : %#v\n", agesExp)
+
+	// note:
+	// ages and agesExp get printed 0x0 because they're byte arrays.
+	// bytes are represented with hex values. 0x0 means 0.
+
+	// =========================================================================
+	// GETTING AND SETTING ARRAY ELEMENTS
+	// =========================================================================
+
+	// Note:
+	//
+	// Since, I've already declared the ages variable above,
+	//   and, to show you the example below, I needed to create a new block.
+	//
+	// ages variable below is in a new block below. So, it's a new variable.
+	//
+	// I did so because I need to change the element type of the ages array
+	//   to int (or, subtracting from a byte results in wraparound).
+	{
+		var ages [2]int
+
+		fmt.Println()
+		fmt.Printf("ages              : %#v\n", ages)
+		fmt.Printf("ages's type       : %T\n", ages)
+
+		fmt.Println("len(ages)         :", len(ages))
+		fmt.Println("ages[0]           :", ages[0])
+		fmt.Println("ages[1]           :", ages[1])
+		fmt.Println("ages[len(ages)-1] :", ages[len(ages)-1])
+
+		// WRONG:
+		// fmt.Println("ages[-1]          :", ages[-1])
+		// fmt.Println("ages[2]           :", ages[2])
+		// fmt.Println("ages[len(ages)]   :", ages[len(ages)])
+
+		ages[0] = 6
+		ages[1] -= 3
+
+		// WRONG:
+		// ages[0] = "Can I?"
+
+		fmt.Println("ages[0]           :", ages[0])
+		fmt.Println("ages[1]           :", ages[1])
+
+		ages[0] *= ages[1]
+		fmt.Println("ages[0]           :", ages[0])
+		fmt.Println("ages[1]           :", ages[1])
+	}
 }