add: slices: last 3 quizzes

16-slices/questions/7-mechanics-of-append.md

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+# The Mechanics of Append Quiz
+
+## Which append call below allocates a new backing array for the following slice?
+```go
+words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
+```
+1. words = append(words[:3], "crystals")
+2. words = append(words[:4], "crystals")
+3. words = append(words[:5], "crystals")
+4. words = append(words[:5], "crystals", "and", "diamonds") *CORRECT*
+
+> **1:** No, it just overwrites the 4th element.
+> 
+> **2:** No, it just overwrites the 5th element.
+> 
+> **3:** No, it just overwrites the last element.
+> 
+> **4:** Yes, it overwrites the last element, then it adds two element. However, there is not enough space to do that, so it allocates a new backing array.
+
+
+## What does the program print?
+```go
+words := []string{"lucy", "in", "the", "sky", "with", "diamonds"}
+words = append(words[:1], "is", "everywhere")
+words = append(words, words[len(words)+1:cap(words)]...)
+```
+1. lucy in the sky with diamonds
+2. lucy is everywhere in the sky with diamonds
+3. lucy is everywhere with diamonds *CORRECT*
+4. lucy is everywhere
+
+> **3:** line #2 overwrites the 2nd and 3rd elements. line #3 appends ["with" "diamonds"] after the ["lucy" "is" "everwhere"].
+
+
+## What are the length and capacity of the words slice?
+```go
+// The words slice has 1023 elements.
+//
+// Tip: The keyed slice works like the same as a keyed array.
+// If you don't remember how it works, please check out the keyed elements in the arrays section.
+//
+words := []string{1022: ""}
+words = append(words, "boom!")
+```
+1. Length: 1024 - Capacity: 1024
+2. Length: 1025 - Capacity: 1025
+3. Length: 1025 - Capacity: 1280
+4. Length: 1024 - Capacity: 2048 *CORRECT*
+
+> **4:** That's right! Append function grows by doubling the capacity of the previous slice.
+
+
+## What are the length and capacity of the words slice?
+```go
+// The words slice has 1024 elements.
+//
+// Tip: The keyed slice works like the same as a keyed array.
+// If you don't remember how it works, please check out the keyed elements in the arrays section.
+//
+words := []string{1023: ""}
+words = append(words, "boom!")
+```
+1. Length: 1024 - Capacity: 1024
+2. Length: 1025 - Capacity: 1025
+3. Length: 1025 - Capacity: 1280 *CORRECT*
+4. Length: 1025 - Capacity: 2048
+
+> **3, 4:** After 1024 elements, the append function grows at a slower rate, about 25%.