分支switch

    2. package main
    4. import (
    5.     "fmt"
    6.     "io/ioutil"
    7. )
    9. func grade(score int) string {
    10.     g := ""
    11.     switch {
    12.     case score < 0 || score > 100:
    13.         panic(fmt.Sprintf(
    14.             "Wrong score: %d", score))
    15.     case score < 60:
    16.         g = "F"
    17.     case score < 80:
    18.         g = "C"
    19.     case score < 90:
    20.         g = "B"
    21.     case score <= 100:
    22.         g = "A"
    23.     }
    24.     return g
    25. }
    27. func main() {
    28.     // If "abc.txt" is not found,
    29.     // please check what current directory is,
    30.     // and change filename accordingly.
    31.     const filename = "abc.txt"
    32.     if contents, err := ioutil.ReadFile(filename); err != nil {
    33.         fmt.Println(err)
    34.     } else {
    35.         fmt.Printf("%s\n", contents)
    36.     }
    38.     //switch
    39.     fmt.Println(
    40.         grade(0),
    41.         grade(59),
    42.         grade(60),
    43.         grade(82),
    44.         grade(99),
    45.         grade(100),
    46.         // Uncomment to see it panics.
    47.         grade(-3),
    48.     )
    49. }

    循环分支

    1. package main
    3. import (
    4.     "bufio"
    5.     "fmt"
    6.     "io"
    7.     "os"
    8.     "strconv"
    9.     "strings"
    10. )
    12. func convertToBin(n int) string {
    13.     result := ""
    14.     for ; n > 0; n /= 2 {
    15.         lsb := n % 2
    16.         result = strconv.Itoa(lsb) + result
    17.     }
    18.     return result
    19. }
    21. func printFile(filename string) {
    22.     file, err := os.Open(filename)
    23.     if err != nil {
    24.         panic(err)
    25.     }
    27.     printFileContents(file)
    28. }
    30. func printFileContents(reader io.Reader) {
    31.     scanner := bufio.NewScanner(reader)
    33.     for scanner.Scan() {
    34.         fmt.Println(scanner.Text())
    35.     }
    36. }
    38. func forever() {
    39.     for {
    40.         fmt.Println("abc")
    41.     }
    42. }
    44. func main() {
    45.     fmt.Println("convertToBin results:")
    46.     fmt.Println(
    47.         convertToBin(5),  // 101
    48.         convertToBin(13), // 1101
    49.         convertToBin(72387885),
    50.         convertToBin(0),
    51.     )
    53.     fmt.Println("abc.txt contents:")
    54.     printFile("basic/branch/abc.txt")
    56.     fmt.Println("printing a string:")
    57.     s := `abc"d"
    58.     kkkk
    59.     123
    60.     p`
    61.     printFileContents(strings.NewReader(s))
    63.     // Uncomment to see it runs forever
    64.     // forever()
    65. }

    函数

    1. package main
    3. import (
    4.     "fmt"
    5.     "math"
    6.     "reflect"
    7.     "runtime"
    8. )
    10. func eval(a, b int, op string) (int, error) {
    11.     switch op {
    12.     case "+":
    13.         return a + b, nil
    14.     case "-":
    15.         return a - b, nil
    16.     case "*":
    17.         return a * b, nil
    18.     case "/":
    19.         q, _ := div(a, b)
    20.         return q, nil
    21.     default:
    22.         return 0, fmt.Errorf(
    23.             "unsupported operation: %s", op)
    24.     }
    25. }
    27. func div(a, b int) (q, r int) {
    28.     return a / b, a % b
    29. }
    31. func apply(op func(int, int) int, a, b int) int {
    32.     p := reflect.ValueOf(op).Pointer()
    33.     opName := runtime.FuncForPC(p).Name()
    34.     fmt.Printf("Calling function %s with args "+
    35.         "(%d, %d)\n", opName, a, b)
    37.     return op(a, b)
    38. }
    40. //可变参数
    41. func sum(numbers ...int) int {
    42.     s := 0
    43.     for i := range numbers {
    44.         s += numbers[i]
    45.     }
    46.     return s
    47. }
    49. func swap(a, b int) (int, int) {
    50.     return b, a
    51. }
    53. func main() {
    54.     fmt.Println("Error handling")
    55.     if result, err := eval(3, 4, "x"); err != nil {
    56.         fmt.Println("Error:", err)
    57.     } else {
    58.         fmt.Println(result)
    59.     }
    60.     q, r := div(13, 3)
    61.     fmt.Printf("13 div 3 is %d mod %d\n", q, r)
    63.     // 函数式编程
    64.     fmt.Println("pow(3, 4) is:", apply(
    65.         func(a int, b int) int {
    66.             return int(math.Pow(
    67.                 float64(a), float64(b)))
    68.         }, 3, 4))
    70.     fmt.Println("1+2+...+5 =", sum(1, 2, 3, 4, 5))
    72.     a, b := 3, 4
    73.     a, b = swap(a, b)
    74.     fmt.Println("a, b after swap is:", a, b)
    75. }

    image.jpeg