平时练习Go的代码

package main

import "fmt"

func main() {
	var result = sum(10)
	fmt.Printf("sum(%d) is: %d\n", 10, result)

}

// sum 计算 0+1+2+...+n 的累加和
func sum(n int) (res int) {
	if n <= 0 {
		res = 0
	}else {
		res = n + sum(n-1)
	}
	return
}

package main

import "fmt"

func main()  {
	callback(1,Add)
}

func Add(a,b int)  {
	fmt.Printf("The sum of %d and %d is: %d\n", a, b, a+b)
}

func callback(y int,f func(int,int))  {
	f(y,2)
}

package main

import "fmt"

func main() {
	var f = Adder2()
	fmt.Print(f(1), " - ")
	fmt.Print(f(20), " - ")
	fmt.Print(f(300))
}

func Adder2() func(int) int {
	var x int
	return func(delta int) int {
		x += delta
		return x
	}
}

package main

import "fmt"

func main() {
	// make an Add2 function, give it a name p2, and call it:
	p2 := Add2()
	fmt.Printf("Call Add2 for 3 gives: %v\n", p2(3))
	// make a special Adder function, a gets value 3:
	TwoAdder := Adder(2)
	fmt.Printf("The result is: %v\n", TwoAdder(3))
}

func Add2() func(b int) int {
	return func(b int) int {
		return b + 2
	}
}

func Adder(a int) func(b int) int {
	return func(b int) int {
		return a + b
	}
}

package main
import "fmt"

func main() {
	var arr1 [6]int
	var slice1 []int = arr1[2:5] // item at index 5 not included!

	// load the array with integers: 0,1,2,3,4,5
	for i := 0; i < len(arr1); i++ {
		arr1[i] = i
	}

	// print the slice
	for i := 0; i < len(slice1); i++ {
		fmt.Printf("Slice at %d is %d\n", i, slice1[i])
	}

	fmt.Printf("The length of arr1 is %d\n", len(arr1))
	fmt.Printf("The length of slice1 is %d\n", len(slice1))
	fmt.Printf("The capacity of slice1 is %d\n", cap(slice1))

	// grow the slice
	slice1 = slice1[0:4]
	for i := 0; i < len(slice1); i++ {
		fmt.Printf("Slice at %d is %d\n", i, slice1[i])
	}
	fmt.Printf("The length of slice1 is %d\n", len(slice1))
	fmt.Printf("The capacity of slice1 is %d\n", cap(slice1))

	// grow the slice beyond capacity
	//slice1 = slice1[0:7 ] // panic: runtime error: slice bound out of range
}