Go exercise 2-map operations

func T2_1() {

// Key value string, value int type

    m1 := map[string]int{}

// Add an element

    m1["str1"] = 1

    fmt.Println(m1)

// Directly Overwrite

    m1["str1"] = 2

    fmt.Println(m1)

If V, OK: = m1 ["str1"]; OK {// determine whether the key exists.

        fmt.Println(v)

    }

FMT. println (m1 ["C"]) // for keys that do not exist, \ 0 is returned directly without error.

Delete (M1, "str1") // delete an element

    fmt.Println(m1)

// Run the make function in advance? A reasonable element quantity parameter helps improve performance.

// Because of preapproval? I? Large memory to avoid frequent expansion during subsequent operations.

    m2 := make(map[string]int, 1000)

    m2["str2"] = 200

    fmt.Println(m2)

// Len returns the number of actually stored elements. CAP does not work.

    fmt.Println(len(m2))

}

Go exercise 2-map operations