golang map 取り扱い 再履修

package main

import (
	"fmt"
)

// (1)
var m = make(map[int]int)  // (2)をコメントアウトするならこっちを使う

func main() {

	// (2)
	//m := map[int]int{} // (1)をコメントアウトするならこっちを使う

	m[3124] = 9
	m[1992] = 2
	m[2020] = 3

	// キーのみ取り出す
	for key := range m {
		fmt.Println(key)
	}

	//3124
	//1992
	//2020

	fmt.Println()

	// キーと値
	for key, value := range m {
		fmt.Println(key, value)
	}
	fmt.Println()

	//1992 2
	//2020 3
	//3124 9

	// 値のみ必要な場合
	for _, value := range m {
		fmt.Println(value)
	}

	//9
	//2
	//3

	fmt.Println()

	// ループの回数を数える
	i := 0
	for key, value := range m {
		fmt.Println(key, value)
		i++
	}

	//3124 9
	//1992 2
	//2020 3

	fmt.Println()
	fmt.Println("delete(m, 1992)")
	delete(m, 1992)
	for key, value := range m {
		fmt.Println(key, value)
	}

	//delete(m, 1992)
	//2020 3
	//3124 9


	fmt.Println()
	fmt.Println("add as m[2999] = 2")
	m[2999] = 2
	for key, value := range m {
		fmt.Println(key, value)
	}

	//add as m[2999] = 2
	//3124 9
	//2999 2
	//2020 3

	_, ok := m[100]
	if ok {
		fmt.Println("OK")
	} else {
		fmt.Println("NG")
	}

	// NG

	_, ok = m[2999]
	if ok {
		fmt.Println("OK")
	} else {
		fmt.Println("NG")
	}

	// OK

	fmt.Println(m)
	// map[2020:3 2999:2 3124:9]

	m[2020]++

	fmt.Println(m)
	// map[2020:4 2999:2 3124:9]



}