链表显示功能不正常

Question

When I call the display function, the first element of linked list is printed twice. I do not know what is wrong with the code. Please help me to figure it out. The code is as follows:

#include <iostream>
using namespace std;
class node{
public:
    char data;
    node *link;
};

class linklist{
    private:
        node *start, *temp, *cur;
    public:
        linklist(){
            start = NULL;
        }
        void insert(char x){
            if (start == NULL){
                start = new node;
                start->data = x;
                start->link = NULL;
                cur = start;
            }
            else
            while (cur->link != NULL){
                cur = cur->link;
            }

                temp = new node;
                temp->data = x;
                temp->link = NULL;
                cur->link = temp;

        }
        void display(){
            cur = start;

            while (cur->link != NULL){  
                cout << "Value is: " << cur->data << endl;
                cur = cur->link;
            }
            cout << "Value is: " << cur->data << endl;
        }
};
int main(){
    linklist obj;
    obj.insert('e');
    obj.insert('t');
    obj.insert('r');
    obj.insert('w');
    obj.insert('l');
    obj.display();

    system("Pause");
}

the expected output is: etrwl .
Actual output: eetrwl

Answer 1

You have two problems with your code. The first is the missing {...} surrounding your else statement in insert() . In order to have the needed code only apply to the else case, you need to surround the entire else case with braces, eg:

        else {
            while (cur->link != NULL) {
                cur = cur->link;
            }
            temp = new node;
            temp->data = x;
            temp->link = NULL;
            cur->link = temp;
        }
    }

Secondly, your conditional used for display() is incorrect. You only want to output the contents when cur != NULL not when cur->next != NULL (that is why you tried to tack an extra output statement following the end of the loop to catch your last value). Don't do that, if you find yourself trying to do something like that -- your are probably doing it wrong.

With that change, you simply have:

    void display() {
        cur = start;
        while (cur != NULL) {  
            cout << "Value is: " << cur->data << endl;
            cur = cur->link;
        }
    }

Putting it altogether, you have:

#include <iostream>

using namespace std;

class node{
public:
    char data;
    node *link;
};

class linklist{
private:
    node *start, *temp, *cur;
public:
    linklist() {
        start = NULL;
    }

    void insert (char x) {
        if (start == NULL) {
            start = new node;
            start->data = x;
            start->link = NULL;
            cur = start;
        }
        else {
            while (cur->link != NULL) {
                cur = cur->link;
            }
            temp = new node;
            temp->data = x;
            temp->link = NULL;
            cur->link = temp;
        }
    }

    void display() {
        cur = start;
        while (cur != NULL) {  
            cout << "Value is: " << cur->data << endl;
            cur = cur->link;
        }
    }
};

int main (void) {

    linklist obj;

    obj.insert('e');
    obj.insert('t');
    obj.insert('r');
    obj.insert('w');
    obj.insert('l');
    obj.display();

    system("Pause");
}

Example Use/Output

$ ./bin/llinsert
Value is: e
Value is: t
Value is: r
Value is: w
Value is: l

Look things over an let me know if you have further questions.