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golang

1. hello world

package main // head of file 

import "fmt"

func main() {
    fmt.Println("hello world")
}

out put:

hello world

2. Values

package main

import "fmt"

func main() {

    fmt.Println("go" + "lang")

    fmt.Println("1+1 =", 1+1)
    fmt.Println("7.0/3.0 =", 7.0/3.0)

    fmt.Println(true && false)
    fmt.Println(true || false)
    fmt.Println(!true)
}

out put:

golang
1+1 = 2
7.0/3.0 = 2.3333333333333335
false
true
false

3. Variables

package main

import "fmt"

func main() {

    var a = "initial"
    fmt.Println(a)

    var b, c int = 1, 2
    fmt.Println(b, c)

    var d = true
    fmt.Println(d)

    var e int
    fmt.Println(e)

    f := "apple"
    fmt.Println(f)
}

out put:

initial
1 2
true
0
apple

4. Constants

package main

import (
    "fmt"
    "math"
)

const s string = "constant"

func main() {
    fmt.Println(s)

    const n = 500000000

    const d = 3e20 / n
    fmt.Println(d)

    fmt.Println(int64(d))

    fmt.Println(math.Sin(n))
}

out put:

constant
6e+11
600000000000
-0.28470407323754404

5. For

package main

import "fmt"

func main() {

    i := 1
    for i <= 3 {
        fmt.Println(i)
        i = i + 1
    }

    for j := 0; j < 3; j++ {
        fmt.Println(j)
    }

    for i := range 3 {
        fmt.Println("range", i)
    }

    for {
        fmt.Println("loop")
        break
    }

    for n := range 6 {
        if n%2 == 0 {
            continue
        }
        fmt.Println(n)
    }
}

out put:

1
2
3
0
1
2
range 0
range 1
range 2
loop
1
3
5

6. If/Else

package main

import "fmt"

func main() {

    if 7%2 == 0 {
        fmt.Println("7 is even")
    } else {
        fmt.Println("7 is odd")
    }

    if 8%4 == 0 {
        fmt.Println("8 is divisible by 4")
    }

    if 8%2 == 0 || 7%2 == 0 {
        fmt.Println("either 8 or 7 are even")
    }

    if num := 9; num < 0 {
        fmt.Println(num, "is negative")
    } else if num < 10 {
        fmt.Println(num, "has 1 digit")
    } else {
        fmt.Println(num, "has multiple digits")
    }
}

out put:

7 is odd
8 is divisible by 4
either 8 or 7 are even
9 has 1 digit

7. Switch

package main

import (
    "fmt"
    "time"
)

func main() {

    i := 2
    fmt.Print("Write ", i, " as ")
    switch i {
    case 1:
        fmt.Println("one")
    case 2:
        fmt.Println("two")
    case 3:
        fmt.Println("three")
    }

    switch time.Now().Weekday() {
    case time.Saturday, time.Sunday:
        fmt.Println("It's the weekend")
    default:
        fmt.Println("It's a weekday")
    }

    t := time.Now()
    switch {
    case t.Hour() < 12:
        fmt.Println("It's before noon")
    default:
        fmt.Println("It's after noon")
    }

    whatAmI := func(i interface{}) {
        switch t := i.(type) {
        case bool:
            fmt.Println("I'm a bool")
        case int:
            fmt.Println("I'm an int")
        default:
            fmt.Printf("Don't know type %T\n", t)
        }
    }
    whatAmI(true)
    whatAmI(1)
    whatAmI("hey")
}

out put:

Write 2 as two
It's a weekday
It's after noon
I'm a bool
I'm an int
Don't know type string

8. Arrays

package main

import "fmt"

func main() {

    var a [5]int
    fmt.Println("emp:", a)

    a[4] = 100
    fmt.Println("set:", a)
    fmt.Println("get:", a[4])

    fmt.Println("len:", len(a))

    b := [5]int{1, 2, 3, 4, 5}
    fmt.Println("dcl:", b)

    b = [...]int{1, 2, 3, 4, 5}
    fmt.Println("dcl:", b)

    b = [...]int{100, 3: 400, 500}
    fmt.Println("idx:", b)

    var twoD [2][3]int
    for i := 0; i < 2; i++ {
        for j := 0; j < 3; j++ {
            twoD[i][j] = i + j
        }
    }
    fmt.Println("2d: ", twoD)

    twoD = [2][3]int{
        {1, 2, 3},
        {1, 2, 3},
    }
    fmt.Println("2d: ", twoD)
}

out put:

emp: [0 0 0 0 0]
set: [0 0 0 0 100]
get: 100
len: 5
dcl: [1 2 3 4 5]
dcl: [1 2 3 4 5]
idx: [100 0 0 400 500]
2d:  [[0 1 2] [1 2 3]]
2d:  [[1 2 3] [1 2 3]]

9. Slices

package main

import (
    "fmt"
    "slices"
)

func main() {

    var s []string
    fmt.Println("uninit:", s, s == nil, len(s) == 0)

    s = make([]string, 3)
    fmt.Println("emp:", s, "len:", len(s), "cap:", cap(s))

    s[0] = "a"
    s[1] = "b"
    s[2] = "c"
    fmt.Println("set:", s)
    fmt.Println("get:", s[2])

    fmt.Println("len:", len(s))

    s = append(s, "d")
    s = append(s, "e", "f")
    fmt.Println("apd:", s)

    c := make([]string, len(s))
    copy(c, s)
    fmt.Println("cpy:", c)

    l := s[2:5]
    fmt.Println("sl1:", l)

    l = s[:5]
    fmt.Println("sl2:", l)

    l = s[2:]
    fmt.Println("sl3:", l)

    t := []string{"g", "h", "i"}
    fmt.Println("dcl:", t)

    t2 := []string{"g", "h", "i"}
    if slices.Equal(t, t2) {
        fmt.Println("t == t2")
    }

    twoD := make([][]int, 3)
    for i := 0; i < 3; i++ {
        innerLen := i + 1
        twoD[i] = make([]int, innerLen)
        for j := 0; j < innerLen; j++ {
            twoD[i][j] = i + j
        }
    }
    fmt.Println("2d: ", twoD)
}

out put:

uninit: [] true true
emp: [  ] len: 3 cap: 3
set: [a b c]
get: c
len: 3
apd: [a b c d e f]
cpy: [a b c d e f]
sl1: [c d e]
sl2: [a b c d e]
sl3: [c d e f]
dcl: [g h i]
t == t2
2d:  [[0] [1 2] [2 3 4]]

10. maps:

package main

import (
	"fmt"
	"maps"
)

func main() {

	m := make(map[string]int)

	m["k1"] = 7
	m["k2"] = 13

	fmt.Println("1. map:", m)

	v1 := m["k1"]
	fmt.Println("2. v1:", v1)

	v3 := m["k3"]
	fmt.Println("3. v3:", v3)

	fmt.Println("4. len:", len(m))

	delete(m, "k2")
	fmt.Println("5. map:", m)

	clear(m)
	fmt.Println("6. map:", m)

	prs := m["k2"]
	fmt.Println("7. prs:", prs)

	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("8. map:", n)

	n2 := map[string]int{"foo": 1, "bar": 2}
	if maps.Equal(n, n2) {
		fmt.Println("9. n == n2")
	}
}

out put:

map: map[k1:7 k2:13]
v1: 7
v3: 0
len: 2
map: map[k1:7]
map: map[]
prs: false
map: map[bar:2 foo:1]
n == n2