Using user input to define array

Question

I have a project where I need to create a shopping list with checkout functionality. I am trying to create an array using a users input. They supply how many products they are purchasing and I need to use that to define the size of the array.

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

struct shopList {
    double pluCode;
    string product;
    int saleType; // 0 = per unit, 1 = per pound
    double price;
    double inventory;


};

int main(){

    char line[255];
    const int items = 0;
    int n;

    ofstream outfile;
    outfile.open("products.txt");

    cout << "How many items in your checkout: ";
    cin >> items;

    shopList shop[items];

    for (n = 0; n < items; n++) {
        cout << "Enter the PLU code: ";
        cin >> shop.pluCode;
        outfile << shop.pluCode << " ";

        cout << "Enter product name: ";
        cin >> shop.product;
        outfile << shop.product << " ";

        cout << "Enter the price type (0 for per unit, 1 for per pound): ";
        cin >> shop.saleType;
        outfile << shop.saleType << " ";

        cout << "Enter the price of the product: ";
        cin >> shop.price;
        outfile << shop.price << " ";

        cout << "How much will you purchase: ";
        cin >> shop.inventory;
        outfile << shop.inventory << " " << "\n";

    }



    outfile.close();

    ifstream infile;
    infile.open("products.txt");
    infile.getline(line, 255);
    cout << line << endl;
}

You can't do that in standard C++. Use std::vector (or possibly allocate using new) — Mats Petersson
– Mats Petersson, Commented Mar 4, 2015 at 20:28
@MatsPetersson I'm quite sure "can't do that in standard C++" is false. You've said why in your own comment. — Paweł Stawarz
– Paweł Stawarz, Commented Mar 4, 2015 at 20:38
@PawełStawarz: No, you can't use variable length arrays in C++. There are ALTERNATIVE solutions that solve the same problem. — Mats Petersson
– Mats Petersson, Commented Mar 4, 2015 at 20:50
@MatsPetersson I can't agree with you. There's no mention about VLAs in the question itself, you're judging that's the case only because of how the author tried to implement it. The question is "I need to use that [user input] to define the size of the array.", and the answer most certainly isn't "can't do that" :) — Paweł Stawarz
– Paweł Stawarz, Commented Mar 4, 2015 at 22:07

01axel01christian · Accepted Answer · 2015-03-04 20:37:18Z

1

It's possible , you just have to change your declaration like that;

int items = 0 ; cin >> items;

shopList *shop =  new  shopList [items];

answered Mar 4, 2015 at 20:37

01axel01christian

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5 Comments

Thomas Matthews Over a year ago

Remember to use delete [] shop; to deallocate the array.

Aaron Havenar Over a year ago

@sexobert How would I change "cin >> shop.pluCode;" to adjust? It is giving me "Error: expression must have class type".

01axel01christian Over a year ago

Of course , don't forget to " delete [] shop " after using your array

01axel01christian Over a year ago

@AaronHavenar , your variable shop is a pointer to a shopList array. shop is an array, so you must do some thing like that shop[n].pluCode (where i is a counter) instead of shop.pluCode;

01axel01christian Over a year ago

@AaronHavenar You have to use this syntax everywhere you want to use your array. shop[n]."witch attributes of your shopList structure" ;

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