04.4.1.md

eBook/examples/chapter_4/alias.go

@@ -1,6 +1,7 @@
 package main
-import fm "fmt" // alias3
 
-func main() {
-    fm.Println("hello, world")
+import fm "fmt"  // alias
+
+func main() { 
+	fm.Println("hello, world")
 }

eBook/examples/chapter_4/casting.go

@@ -0,0 +1,18 @@
+package main
+import "fmt"
+
+func main() {
+	var n int16 = 34
+	var m int32
+	
+// compiler error: cannot use n (type int16) as type int32 in assignment
+	//m = n 
+	m = int32(n)
+	
+	fmt.Printf("32 bit int is:  %d\n", m)
+	fmt.Printf("16 bit int is:  %d\n", n)
+}
+/* Output:
+32 bit int is:  34
+16 bit int is:  34
+*/

eBook/examples/chapter_4/char.go

@@ -0,0 +1,22 @@
+// char.go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	var ch int = '\u0041'
+	var ch2 int = '\u03B2' 
+	var ch3 int = '\U00101234'
+	fmt.Printf("%d - %d - %d\n", ch, ch2, ch3)
+	fmt.Printf("%c - %c - %c\n", ch, ch2, ch3)
+	fmt.Printf("%X - %X - %X\n", ch, ch2, ch3)
+	fmt.Printf("%U - %U - %U", ch, ch2, ch3)
+}
+/* Ouput: 
+65 - 946 - 1053236
+A - β - 􁈴
+41 - 3B2 - 101234
+U+0041 - U+03B2 - U+101234
+*/

eBook/examples/chapter_4/count_substring.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	var str string = "Hello, how is it going, Hugo?"
+	var manyG = "gggggggggg"
+
+	fmt.Printf("Number of H's in %s is: ", str)
+	fmt.Printf("%d\n", strings.Count(str, "H"))
+
+	fmt.Printf("Number of double g's in %s is: ", manyG)
+	fmt.Printf("%d\n", strings.Count(manyG, "gg"))
+}

eBook/examples/chapter_4/goos.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	var goos string = os.Getenv("GOOS")
+	fmt.Printf("The operating system is: %s\n", goos)
+	path := os.Getenv("PATH")  
+    fmt.Printf("Path is %s\n", path)
+}

eBook/examples/chapter_4/gotemplate.go

@@ -1,7 +1,7 @@
 package main
 
 import (
-   "fmt"
+	"fmt"
 )
 
 const c = "C"
@@ -10,20 +10,21 @@ var v int = 5
 
 type T struct{}
 
-func init() { // initialization of package
+func init() {
+	// initialization of package
 }
 
 func main() {
-    var a int
-    Func1()
-    // ...
-    fmt.Println(a)
+	var a int
+	Func1()
+	// ...
+	fmt.Println(a)
 }
 
 func (t T) Method1() {
-    //...
+	//...
 }
 
 func Func1() { // exported function Func1
-    //...
+	//...
 }

eBook/examples/chapter_4/hello_world.go

@@ -1,9 +1,7 @@
-// hello_world.go
 package main
 
-import "fmt"
+import "fmt"  
 
-func main() {
+func main() { 
 	fmt.Println("hello, world")
 }
-

eBook/examples/chapter_4/hello_world2.go

@@ -3,6 +3,5 @@ package main
 import "fmt" // Package implementing formatted I/O.
 
 func main() {
-    fmt.Printf("Καλημέρα κόσμε; or こんにちは 世界\n")
+	fmt.Printf("Hello, world; or Καλημέρα κόσμε; or こんにちは 世界\n")
 }
-

eBook/examples/chapter_4/index_in_string.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	var str string = "Hi, I'm Marc, Hi."
+
+	fmt.Printf("The position of \"Marc\" is: ")
+	fmt.Printf("%d\n", strings.Index(str, "Marc"))
+
+	fmt.Printf("The position of the first instance of \"Hi\" is: ")
+	fmt.Printf("%d\n", strings.Index(str, "Hi"))
+	fmt.Printf("The position of the last instance of \"Hi\" is: ")
+	fmt.Printf("%d\n", strings.LastIndex(str, "Hi"))
+
+	fmt.Printf("The position of \"Burger\" is: ")
+	fmt.Printf("%d\n", strings.Index(str, "Burger"))
+}

eBook/examples/chapter_4/init.go

@@ -0,0 +1,9 @@
+package trans
+
+import "math"
+
+var Pi float64
+
+func init() {
+	Pi = 4 * math.Atan(1) // init() function computes Pi
+}

eBook/examples/chapter_4/pointer.go

@@ -0,0 +1,12 @@
+package main
+
+import "fmt"
+
+func main() {
+	var i1 = 5
+	fmt.Printf("An integer: %d, its location in memory: %p\n", i1, &i1)
+
+	var intP *int
+	intP = &i1
+	fmt.Printf("The value at memory location %p is %d\n", intP, *intP) 
+}

eBook/examples/chapter_4/presuffix.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	var str string = "This is an example of a string"
+
+	fmt.Printf("T/F? Does the string \"%s\" have prefix %s? ", str, "Th")
+	fmt.Printf("%t\n", strings.HasPrefix(str, "Th"))
+}
+// Output: T/F? Does the string "This is an example of a string" have prefix Th? true

eBook/examples/chapter_4/random.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+)
+
+func main() {
+	for i := 0; i < 10; i++ {
+		a := rand.Int()
+		fmt.Printf("%d / ", a)
+	}
+	for i := 0; i < 5; i++ {
+		r := rand.Intn(8)
+		fmt.Printf("%d / ", r)
+	}
+	fmt.Println()
+	timens := int64(time.Now().Nanosecond())
+	rand.Seed(timens)
+	for i := 0; i < 10; i++ {
+		fmt.Printf("%2.2f / ", 100*rand.Float32())
+	}
+}
+/* Output:
+134020434 / 1597969999 / 1721070109 / 2068675587 / 1237770961 / 220031192 / 2031484958 / 583324308 / 958990240 / 413002649 / 6 / 7 / 2 / 1 / 0 / 
+22.84 / 10.12 / 44.32 / 58.58 / 15.49 / 12.23 / 30.16 / 88.48 / 34.26 / 27.18 / 
+*/

eBook/examples/chapter_4/repeat_string.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	var origS string = "Hi there! "
+	var newS string
+
+	newS = strings.Repeat(origS, 3)
+	fmt.Printf("The new repeated string is: %s\n", newS)
+}

eBook/examples/chapter_4/string_conversion.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func main() {
+	var orig string = "666"
+	var an int
+	var newS string
+
+	fmt.Printf("The size of ints is: %d\n", strconv.IntSize)	  
+
+	an, _ = strconv.Atoi(orig)
+	fmt.Printf("The integer is: %d\n", an) 
+	an = an + 5
+	newS = strconv.Itoa(an)
+	fmt.Printf("The new string is: %s\n", newS)
+}

eBook/examples/chapter_4/string_pointer.go

@@ -0,0 +1,13 @@
+package main
+
+import "fmt"
+
+func main() {
+	s := "good bye"
+	var p *string = &s
+	*p = "ciao"
+
+	fmt.Printf("Here is the pointer p: %p\n", p)  // prints address
+	fmt.Printf("Here is the string *p: %s\n", *p) // prints string
+	fmt.Printf("Here is the string  s: %s\n", s)  // prints same string
+}

eBook/examples/chapter_4/strings_splitjoin.go

@@ -0,0 +1,33 @@
+// strings.go
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	str := "The quick brown fox jumps over the lazy dog"
+	sl := strings.Fields(str)
+	fmt.Printf("Splitted in slice: %v\n", sl)
+	for _, val := range sl {
+		fmt.Printf("%s - ", val)
+	}
+	fmt.Println()
+	str2 := "GO1|The ABC of Go|25"
+	sl2 := strings.Split(str2, "|")
+	fmt.Printf("Splitted in slice: %v\n", sl2)
+	for _, val := range sl2 {
+		fmt.Printf("%s - ", val)
+	}
+	fmt.Println()
+	str3 := strings.Join(sl2,";")
+	fmt.Printf("sl2 joined by ;: %s\n", str3)
+}
+/* Output:
+Splitted in slice: [The quick brown fox jumps over the lazy dog]
+The - quick - brown - fox - jumps - over - the - lazy - dog -
+Splitted in slice: [GO1 The ABC of Go 25]
+GO1 - The ABC of Go - 25 -
+sl2 joined by ;: GO1;The ABC of Go;25
+*/

eBook/examples/chapter_4/testcrash.go

@@ -0,0 +1,11 @@
+// testcrash.go
+// compiles , but crashes
+package main
+
+func main() {
+	var p *int = nil
+	*p = 0
+
+}
+// in Windows: stops only with: <exit code="-1073741819" msg="process crashed"/>
+// runtime error: invalid memory address or nil pointer dereference

eBook/examples/chapter_4/time.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+var week time.Duration
+
+func main() {
+	t := time.Now()
+	fmt.Println(t)     // Wed Dec 21 09:52:14 +0100 RST 2011
+	fmt.Printf("%02d.%02d.%4d\n", t.Day(), t.Month(), t.Year()) // 21.12.2011
+	t = time.Now().UTC()
+	fmt.Println(t)          // Wed Dec 21 08:52:14 +0000 UTC 2011
+	fmt.Println(time.Now()) // Wed Dec 21 09:52:14 +0100 RST 2011
+	// calculating times:
+	week = 60 * 60 * 24 * 7 * 1e9  // must be in nanosec
+	week_from_now := t.Add(week)
+	fmt.Println(week_from_now)      // Wed Dec 28 08:52:14 +0000 UTC 2011
+	// formatting times:
+	fmt.Println(t.Format(time.RFC822))     // 21 Dec 11 0852 UTC
+	fmt.Println(t.Format(time.ANSIC))      // Wed Dec 21 08:56:34 2011
+	fmt.Println(t.Format("02 Jan 2006 15:04")) // 21 Dec 2011 08:52
+	s := t.Format("20060102")
+	fmt.Println(t, "=>", s) // Wed Dec 21 08:52:14 +0000 UTC 2011 => 20111221
+}

eBook/examples/chapter_4/toupper_lower.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	var orig string = "Hey, how are you George?"
+	var lower string
+	var upper string
+
+	fmt.Printf("The original string is: %s\n", orig)
+	lower = strings.ToLower(orig)
+	fmt.Printf("The lowercase string is: %s\n", lower)
+	upper = strings.ToUpper(orig)
+	fmt.Printf("The uppercase string is: %s\n", upper)
+}

eBook/examples/chapter_4/type.go

@@ -0,0 +1,11 @@
+package main
+
+import "fmt"
+
+type TZ int
+
+func main() {
+	var a, b TZ = 3, 4
+	c := a + b
+	fmt.Printf("c has the value: %d", c)
+}

eBook/examples/chapter_4/type_mixing.go

@@ -0,0 +1,9 @@
+package main
+
+func main() {
+	var a int
+	var b int32
+	a = 15
+	b = a + a	 // compiler error
+	b = b + 5    // ok: 5 is a constant 
+}

eBook/examples/chapter_4/use_init.go

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"fmt"
+	"./trans"
+)
+
+var twoPi = 2 * trans.Pi // decl computes twoPi
+
+func main() {
+	fmt.Printf("2*Pi = %g\n", twoPi) // 2*Pi = 6.283185307179586
+}