add: quiz and exercises to pointers

26-pointers/exercises/01-basics/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+// ---------------------------------------------------------
+// EXERCISE: Basics
+//
+//  Let's warm up with the pointer basics. Please follow the
+//  instructions inside the code. Run the solution to see
+//  its output if you need to.
+// ---------------------------------------------------------
+
+package main
+
+type computer struct {
+	brand string
+}
+
+func main() {
+	// create a nil pointer with the type of pointer to a computer
+
+	// compare the pointer variable to a nil value, and say it's nil
+
+	// create an apple computer by putting its address to a pointer variable
+
+	// put the apple into a new pointer variable
+
+	// compare the apples: if they are equal say so and print their addresses
+
+	// create a sony computer by putting its address to a new pointer variable
+
+	// compare apple to sony, if they are not equal say so and print their
+	// addresses
+
+	// put apple's value into a new ordinary variable
+
+	// print apple pointer variable's address, and the address it points to
+	// and, print the new variable's addresses as well
+
+	// compare the value that is pointed by the apple and the new variable
+	// if they are equal say so
+
+	// print the values:
+	// the value that is pointed by the apple and the new variable
+
+	// create a new function: change
+	// the func can change the given computer's brand to another brand
+
+	// change sony's brand to hp using the func — print sony's brand
+
+	// write a func that returns the value that is pointed by the given *computer
+	// print the returned value
+
+	// write a new constructor func that returns a pointer to a computer
+	// and call the func 3 times and print the returned values' addresses
+}

26-pointers/exercises/01-basics/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+type computer struct {
+	brand string
+}
+
+func main() {
+	// create a nil pointer with the type of pointer to a computer
+	var null *computer
+
+	// compare the pointer variable to a nil value
+	if null == nil {
+		// , and say it's nil
+		fmt.Println("null computer is nil")
+	}
+
+	// create an apple computer by putting its address to a pointer variable
+	apple := &computer{brand: "apple"}
+
+	// put the apple into a new pointer variable
+	newApple := apple
+
+	// compare the apples: if they are equal
+	if apple == newApple {
+		// say so and print their addresses
+		fmt.Printf("apples are equal          : apple: %p newApple: %p\n",
+			apple, newApple)
+	}
+
+	// create a sony computer by putting its address to a new pointer variable
+	sony := &computer{brand: "sony"}
+
+	// compare apple to sony, if they are not equal
+	if apple != sony {
+		// say so and print their addresses
+		fmt.Printf("apple and sony are inequal: apple: %p sony: %p\n",
+			apple, sony)
+	}
+
+	// put apple's value into a new ordinary variable
+	appleVal := *apple
+
+	// print apple pointer variable's address, and the address it points to
+	// and, print the new variable's addresses as well
+	fmt.Printf("apple                     : %p %p\n", &apple, apple)
+	fmt.Printf("appleVal                  : %p\n", &appleVal)
+
+	// compare the value that is pointed by the apple and the new variable
+	if *apple == appleVal {
+		// if they are equal say so
+		fmt.Println("apple and appleVal are equal")
+
+		// print the values:
+		// the value that is pointed by the apple and the new variable
+		fmt.Printf("apple                     : %+v — appleVal: %+v\n",
+			*apple, appleVal)
+	}
+
+	// change sony's brand to hp using the func
+	change(sony, "hp")
+	// print sony's brand
+	fmt.Printf("sony                      : %s\n", sony.brand)
+
+	// print the returned value
+	fmt.Printf("appleVal                  : %+v\n", valueOf(apple))
+
+	// and call the func 3 times and print the returned values' addresses
+	fmt.Printf("dell's address            : %p\n", newComputer("dell"))
+	fmt.Printf("lenovo's address          : %p\n", newComputer("lenovo"))
+	fmt.Printf("acer's address            : %p\n", newComputer("acer"))
+}
+
+// create a new function: change
+// the func can change the given computer's brand to another brand
+func change(c *computer, brand string) {
+	c.brand = brand
+}
+
+// write a func that returns the value that is pointed by the given *computer
+func valueOf(c *computer) computer {
+	return *c
+}
+
+// write a new constructor func that returns a pointer to a computer
+func newComputer(brand string) *computer {
+	return &computer{brand: brand}
+}

26-pointers/exercises/02-swap/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+// ---------------------------------------------------------
+// EXERCISE: Swap
+//
+//  Using funcs, swap values through pointers, and swap
+//  the addresses of the pointers.
+//
+//
+//  1- Swap the values through a func
+//
+//     a- Declare two float variables
+//
+//     b- Declare a func that can swap the variables' values
+//        through their memory addresses
+//
+//     c- Pass the variables' addresses to the func
+//
+//     d- Print the variables
+//
+//
+//  2- Swap the addresses of the float pointers through a func
+//
+//     a- Declare two float pointer variables and,
+//        assign them the addresses of float variables
+//
+//     b- Declare a func that can swap the addresses
+//        of two float pointers
+//
+//     c- Pass the pointer variables to the func
+//
+//     d- Print the addresses, and values that are
+//        pointed by the pointer variables
+//
+// ---------------------------------------------------------
+
+package main
+
+func main() {
+}

26-pointers/exercises/02-swap/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+func main() {
+	a, b := 3.14, 6.28
+	swap(&a, &b)
+	fmt.Printf("a : %g — b : %g\n", a, b)
+
+	pa, pb := &a, &b
+	pa, pb = swapAddr(pa, pb)
+	fmt.Printf("pa: %p — pb: %p\n", pa, pb)
+	fmt.Printf("pa: %g — pb: %g\n", *pa, *pb)
+}
+
+func swap(a, b *float64) {
+	*a, *b = *b, *a
+}
+
+func swapAddr(a, b *float64) (*float64, *float64) {
+	return b, a
+}

26-pointers/exercises/03-fix-the-crash/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+// ---------------------------------------------------------
+// EXERCISE: Fix the crash
+//
+// EXPECTED OUTPUT
+//
+//   brand: apple
+// ---------------------------------------------------------
+
+package main
+
+import "fmt"
+
+type computer struct {
+	brand *string
+}
+
+func main() {
+	var c *computer
+	change(c, "apple")
+	fmt.Printf("brand: %s\n", c.brand)
+}
+
+func change(c *computer, brand string) {
+	(*c.brand) = brand
+}

26-pointers/exercises/03-fix-the-crash/solution/main.go

@@ -0,0 +1,24 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+type computer struct {
+	brand *string
+}
+
+func main() {
+	c := &computer{} // init with a value (before: c was nil)
+	change(c, "apple")
+	fmt.Printf("brand: %s\n", *c.brand) // print the pointed value
+}
+
+func change(c *computer, brand string) {
+	c.brand = &brand // set the brand's address
+}

26-pointers/exercises/04-simplify/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+// ---------------------------------------------------------
+// EXERCISE: Simplify the code
+// HINT    : Remove the unnecessary pointer usages
+// ---------------------------------------------------------
+
+package main
+
+import "fmt"
+
+func main() {
+	var schools []map[int]string
+
+	schools = append(schools, make(map[int]string))
+	load(&schools[0], &([]string{"batman", "superman"}))
+
+	schools = append(schools, make(map[int]string))
+	load(&schools[1], &([]string{"spiderman", "wonder woman"}))
+
+	fmt.Println(schools[0])
+	fmt.Println(schools[1])
+}
+
+func load(m *map[int]string, students *[]string) {
+	for i, name := range *students {
+		(*m)[i+1] = name
+	}
+}

26-pointers/exercises/04-simplify/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+func main() {
+	schools := make([]map[int]string, 2)
+	for i := range schools {
+		schools[i] = make(map[int]string)
+	}
+
+	load(schools[0], []string{"batman", "superman"})
+	load(schools[1], []string{"spiderman", "wonder woman"})
+
+	fmt.Println(schools[0])
+	fmt.Println(schools[1])
+}
+
+func load(m map[int]string, students []string) {
+	for i, name := range students {
+		m[i+1] = name
+	}
+}

26-pointers/exercises/05-log-parser/log.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org 4
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

26-pointers/exercises/05-log-parser/log_err_missing.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

26-pointers/exercises/05-log-parser/log_err_negative.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org -100
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

26-pointers/exercises/05-log-parser/log_err_str.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org FOUR
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

26-pointers/exercises/05-log-parser/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+)
+
+func main() {
+	p := newParser()
+
+	// Scan the standard-in line by line
+	in := bufio.NewScanner(os.Stdin)
+	for in.Scan() {
+		p.lines++
+
+		parsed, err := parse(p, in.Text())
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+
+		p = update(p, parsed)
+	}
+
+	// Print the visits per domain
+	sort.Strings(p.domains)
+
+	fmt.Printf("%-30s %10s\n", "DOMAIN", "VISITS")
+	fmt.Println(strings.Repeat("-", 45))
+
+	for _, domain := range p.domains {
+		parsed := p.sum[domain]
+		fmt.Printf("%-30s %10d\n", domain, parsed.visits)
+	}
+
+	// Print the total visits for all domains
+	fmt.Printf("\n%-30s %10d\n", "TOTAL", p.total)
+
+	// Let's handle the error
+	if err := in.Err(); err != nil {
+		fmt.Println("> Err:", err)
+	}
+}

26-pointers/exercises/05-log-parser/parser.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// result stores the parsed result for a domain
+type result struct {
+	domain string
+	visits int
+	// add more metrics if needed
+}
+
+// parser keep tracks of the parsing
+type parser struct {
+	sum     map[string]result // metrics per domain
+	domains []string          // unique domain names
+	total   int               // total visits for all domains
+	lines   int               // number of parsed lines (for the error messages)
+}
+
+// newParser constructs, initializes and returns a new parser
+func newParser() parser {
+	return parser{sum: make(map[string]result)}
+}
+
+// parse parses a log line and returns the parsed result with an error
+func parse(p parser, line string) (parsed result, err error) {
+	fields := strings.Fields(line)
+	if len(fields) != 2 {
+		err = fmt.Errorf("wrong input: %v (line #%d)", fields, p.lines)
+		return
+	}
+
+	parsed.domain = fields[0]
+
+	parsed.visits, err = strconv.Atoi(fields[1])
+	if parsed.visits < 0 || err != nil {
+		err = fmt.Errorf("wrong input: %q (line #%d)", fields[1], p.lines)
+		return
+	}
+
+	return
+}
+
+// update updates the parser for the given parsing result
+func update(p parser, parsed result) parser {
+	domain, visits := parsed.domain, parsed.visits
+
+	// Collect the unique domains
+	if _, ok := p.sum[domain]; !ok {
+		p.domains = append(p.domains, domain)
+	}
+
+	// Keep track of total and per domain visits
+	p.total += visits
+
+	// create and assign a new copy of `visit`
+	p.sum[domain] = result{
+		domain: domain,
+		visits: visits + p.sum[domain].visits,
+	}
+
+	return p
+}

26-pointers/exercises/README.md

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+# Pointer Exercises
+
+1. **[Basics](https://github.com/inancgumus/learngo/tree/master/26-pointers/exercises/01-basics)**
+
+    Warm-up and solidify your knowledge of pointers with the basic exercises. This exercise contains 10+ mini exercises in itself.
+
+2. **[Swap](https://github.com/inancgumus/learngo/tree/master/26-pointers/exercises/02-swap)**
+
+    Using funcs, swap the values through pointers, and swap the addresses of pointers. It may be tricky than it sounds.
+
+3. **[Fix the Crash](https://github.com/inancgumus/learngo/tree/master/26-pointers/exercises/03-fix-the-crash)**
+
+    Fix the crashing program. Another tricky exercise.
+
+4. **[Simplify](https://github.com/inancgumus/learngo/tree/master/26-pointers/exercises/04-simplify)**
+
+    Simplify the given code using your knowledge of map, slices, and pointers.
+
+5. **[Rewrite the Log Parser program using pointers](https://github.com/inancgumus/learngo/tree/master/26-pointers/exercises/05-log-parser)**
+
+    You've watched the lecture. Now, try to rewrite the same log parser program using pointers on your own.