C ++-带有链接列表和一次执行一个功能的类的程序

Question

I'm writing some simple c++ management program that has a warehouse class with a list of products stored as Linked list. it has two problems with the output:

1. Output id/s different (but also similar) to the input
2. there're two different print functions but only one execute when running the program (both of them can run if I commented the other)

Since the program compiles without any error, I tried to debug it line by line but can't seem to figure it out

Edit: To be clear this part of a college project and I can't use stuff ready from standard library like (std::vector, std::list, ...) I need to implement the linked list by hand

    #include <iostream>
    #include <iomanip>      // std::setw

            struct product {
                int id;
                int num;
                product* next;
            };

            class warehouse{
            private:
                product* list = new product;
            public:
                warehouse() = default;

                //adding a product to warehouse
                void AddProduct(const int id,const int boxes) {
                    auto* item = new product;
                    auto* tmp = new product;
                    // copy the head of the linked list
                    tmp = list;
                    item->id = id;
                    item->num = boxes;
                    item->next = tmp;
                    //add the the new product at the beginning
                    list = item;
                }

                //print all products
                void printlist() {
                    int i=0;
                    product* tmp;
                    tmp = list;
                    while(list) {
                        i++;
                        std::cout << "item n." << i << "\tid: " << tmp->id << " number of items: " << tmp->num << std::endl;
                        tmp = tmp -> next;
                    }
                }

                //print products that have less than 50 box and need resupply
                void SupplyReport(){
                    product* tmp = new product;
                    tmp = list;
                    int i=0;
                    while(list) {
                        if (tmp->num <= 50) {
                            i++;
                            std::cout << i << ". id:" << tmp->id << std::setw(20) << "N. of Boxes:" << tmp->num << std::endl;
                        }
                        tmp = tmp -> next;
                    }
                    if (i==0)
                        std::cout << "No product/s need re-supply";
                }
            };

            int main(){
                /* Problems:
                 * Generating random id instead of using the given values
                 * Execute only one function at a time meaning if I commented printlist it's print the supply report as expected
                 */
                warehouse w1;
                w1.AddProduct(005,50);
                w1.AddProduct(007,70);
                w1.AddProduct(055,30);
                w1.printlist();
                w1.SupplyReport();
                return 0;
            }

Answer 1

First:

    private:
        product* list = new product;

This is strange. Why are you creating a meaningless product and having list point to it?

Next:

            auto* tmp = new product;
            // copy the head of the linked list
            tmp = list;

Do you want tmp to point to list or do you want it to point to a new product that you create and allocate? It can do either of these two things, but it can't do both -- it's only one pointer. What do you want it to point to?

Next:

        void printlist() {
            int i=0;
            product* tmp;
            tmp = list;
            while(list) {
                i++;
                std::cout << "item n." << i << "\tid: " << tmp->id << " number of items: " << tmp->num << std::endl;
                tmp = tmp -> next;
            }
        }

You have while(list) , but you want while(tmp) .

Last:

        void SupplyReport(){
            product* tmp = new product;
            tmp = list;
            int i=0;
            while(list) {
                if (tmp->num <= 50) {
                    i++;
                    std::cout << i << ". id:" << tmp->id << std::setw(20) << "N. of Boxes:" << tmp->num << std::endl;
                }
                tmp = tmp -> next;
            }
            if (i==0)
                std::cout << "No product/s need re-supply";
        }

Again, you have tmp point to a new products and then you set it equal to list . Do you want tmp to point to the same thing list points to? Or do you want it to point to a new product ? It can't do both.

You again have while(list) when you want while(tmp) .

Answer 2

For reference:

1. Output id/s different (but also similar) to the input

The solution's to simply avoid variables with the first digit 'zero' or maybe convert them back to decimal

The reason behind this behavior was that compilers consider values that start with '0' as Octal literal! which's why the output was different but not random. I wasn't aware of this "feature" and just wanted all id's to look alike

2. there're two different print functions but only one execute when running the program (both of them can run if I commented the other)

Like David's answer, solved just by changing while(list) to while(tmp) which slipped through my mind because I thought there're basically the same.

The fixed code is:

#include <iostream>
#include <iomanip>      // std::setw

struct product {
    int id;
    int num;
    product* next;
};

class warehouse{
private:
    product* list;
public:

    warehouse() = default;

    //adding a product to warehouse
    void AddProduct(const int id,const int boxes) {
        auto* item = new product;
        product* tmp = list;
        item->id = id;
        item->num = boxes;
        item->next = tmp;
        //add the the new product at the beginning
        list = item;
    }

    //print all products
    void printlist() {
        int i=0;
        product* tmp= list;
        while(tmp) {
            i++;
            std::cout << "item n." << i << "\tid: " << tmp->id << std::setw(20) << " number of items: " << tmp->num << std::endl;
            tmp = tmp -> next;
        }
    }

    //print products that have less than 50 box and need resupply
    void SupplyReport(){
        product* tmp = list;
        int i=0;
        while(tmp) {
            if (tmp->num <= 50) {
                i++;
                std::cout << i << ". id:" << tmp->id << std::setw(20) << "N. of Boxes:" << tmp->num << std::endl;
            }
            tmp = tmp -> next;
        }
        if (i==0)
            std::cout << "No product/s need re-supply";
    }
};

int main(){
    warehouse w1{};
    w1.AddProduct(5,50);
    w1.AddProduct(7,70);
    w1.AddProduct(55,30);
    w1.printlist();
    w1.SupplyReport();
    return 0;
}