How to print linked list

Question

Below is the code:

package collection

type List struct {
    head *Node
    tail *Node
}

func (l *List) First() *Node {
    return l.head
}

func (l *List) Push(value int) {
    node := &Node{value: value}
    if l.head == nil { // list is empty
        l.head = node
    } else {
        l.tail.next = node
    }
    l.tail = node
}

func (l *List) String() string {
    var list string
    n := l.First()
    for n != nil {
        list = list + string(n.Value()) + " "
        n = n.Next()
    }
    return list
}

type Node struct {
    value int
    next  *Node
}

func (n *Node) Next() *Node {
    return n.next
}

func (n *Node) Value() int {
    return n.value
}

On debugging, elements get pushed successfully

But for list = list + string(n.Value()) + " ", this is the debug output: list: " "

package main

import (
    "fmt"

    "github.com/myhub/cs61a/collection"
)

func main() {
    l := &collection.List{}
    l.Push(1)
    l.Push(2)
    l.Push(3)
    fmt.Println(l)
}

1) Why list = list + string(n.Value()) + " " does not concat integers?

2) How to support Node for member value of any type?

1) In order to convert an int to a string, you need to use [`strconv.Itoa`](https://pkg.go.dev/strconv?tab=doc#Itoa). There's a [question covering that](https://stackoverflow.com/questions/10105935/how-to-convert-an-int-value-to-string-in-go). 2) That's harder in Go as it doesn't have generics, so you would need to use an `interface{}` (empty interface) to make it work. You would also have make many type assertions. A better way would be using normal slices as they can support many types with type safety — xarantolus, Jun 07 '20 at 06:56
@xarantolus Why `string(n.Value())` is not giving compile time error, when it cannot do type conversion? — overexchange, Jun 07 '20 at 06:57
It does do a type conversion, they're just character values 1, 2, and 3 which are non-printable characters. — Marc, Jun 07 '20 at 07:00
@Marc Got you... character with ascii value(or UTF-8 value may be) 1 is non-printable character, yes — overexchange, Jun 07 '20 at 07:04
@Marc `strconv.Itoa()` does something different from type conversion? — overexchange, Jun 07 '20 at 07:09
Yes, as spelled out in [the docs](https://golang.org/pkg/strconv/#example_Itoa), it returns the string representation of the integer in base 10. — Marc, Jun 07 '20 at 07:13
You can check the [code](https://golang.org/src/strconv/itoa.go) also to find out. — Eklavya, Jun 07 '20 at 07:15

Eklavya · Answer 1 · 2020-06-07T07:09:33.783

1

Use strconv.Itoa() to convert int into string.

list = list + strconv.Itoa(n.Value()) + " "

In a plain conversion, the value is interpreted as a Unicode code point, and the resulting string will contain the character represented by that code point, encoded in UTF-8.

s := string(97) // s == "a"

and for your case 1,2,3 are all non-printable characters

edited Jun 07 '20 at 07:09

answered Jun 07 '20 at 07:01

Eklavya

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How to print linked list

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