How to use a dynamically sized array of structs?

Question

I have to make my homework. It is console application which uses an array of structs that keep information about a computer(brand, year of manufactoring, weight and inventory number). So I wrote a completely working program, but I want to use a dynamic array, because I dont know how many records the user will input.

Is there way to do this. To add new records in array until the user say n/N? Any suggestions?

This is my version of program:

#include "stdafx.h"
#include <iostream>

using namespace std;

struct ComputerInfo
{
    char computerMark[20], invertarNumber[6];
    unsigned int year;
    float weight;
};

ComputerInfo computerArray[300];

ComputerInfo AddComputers(ComputerInfo compterArray[], int counter)
{
    cout << "Enter mark of the computer: ";
    cin >> computerArray[counter].computerMark;

    cout << "Enter year of establish: ";
    cin>> computerArray[counter].year;

    while ((computerArray[counter].year < 1973)
        || (computerArray[counter].year > 2013))
    {
        cout << "INVALID YEAR!!!" << endl;

        cout << "Enter year of establish: ";
        cin>> computerArray[counter].year;
    }

    cout << "Enter computer weidth: ";
    cin >> computerArray[counter].weight;

    cout << "Enter computer invertar number(up to six digits): ";
    cin >> computerArray[counter].invertarNumber;

    return computerArray[counter];
}

void ShowRecords()
{
    int counter = 0;

    while (computerArray[counter].year != 0)
    {
        cout << "Mark: " << computerArray[counter].computerMark << endl;
        cout << "Year: " << computerArray[counter].year << endl;
        cout << "Weidth: " << computerArray[counter].weight << endl;
        cout << "Inv. number: " << computerArray[counter].invertarNumber << endl << endl;

        counter++;
    }
}

void MoreThanTenYearsOld(ComputerInfo computerArray[])
{
    int counter = 0;
    float counterOldComputers = 0;
    float computerPer = 0;

    while (computerArray[counter].year == 0)
    {
        if (computerArray[counter].year <= 2003)
        {
            counterOldComputers++;
        }

        counter++;
    }

    computerPer = counterOldComputers / 3;

    cout << endl;
    cout << "Percantage of old computers is: " << computerPer << endl;
}

int main()
{
    int counter = 0;
    float computerPer = 0;
    char answer = 'y';

    for (int i = 0; i <= 299; i++)
    {
        strcpy(computerArray[i].computerMark,"");
    }

    while((answer == 'Y') || (answer == 'y'))
    {
        computerArray[counter] = AddComputers(computerArray, counter);
        cout << endl;
        cout << "Do you want to enter more records (Y/N): ";
        cin >> answer;
        cout << endl;
        counter++;
    }

    MoreThanTenYearsOld(computerArray);

    return 0;
}

Stop using arrays, start using std::vector.

Some programmer dude
– Some programmer dude

2012-09-10 13:33:13 +00:00
Commented Sep 10, 2012 at 13:33 — Some programmer dude
– Some programmer dude, Commented Sep 10, 2012 at 13:33
Just wonder: Why 1973..2013 range?

PiotrNycz
– PiotrNycz

2012-09-10 14:48:22 +00:00
Commented Sep 10, 2012 at 14:48 — PiotrNycz
– PiotrNycz, Commented Sep 10, 2012 at 14:48

Luchian Grigore · Accepted Answer · 2012-09-10 13:33:51Z

1

Yes. Instead of your array, use

std::vector<ComputerInfo> computerArray;

and you can add as many objects as you want:

ComputerInfo c;
// read the data
computerArray.push_back(c);

now, computerArray[0] will have the info in c.

You'll need to #include <vector>.

Also, instead of char computerMark[20] you can use a std::string.

answered Sep 10, 2012 at 13:33

Luchian Grigore

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12 Comments

Benjamin Bannier Over a year ago

And use std::string inside the vector.

Luchian Grigore Over a year ago

@honk you mean inside ComputerInfo?

Benjamin Bannier Over a year ago

Yes, exactly, to help the autogen'ed copy constructor. But you knew that.

Code-Apprentice Over a year ago

This answer doesn't address the fact that the OP clearly stated he is doing homework and possibly isn't allowed to use STL classes.

juanchopanza Over a year ago

@Code-Guru there is nothing in the question to suggest any such restrictions. In the absence of more information, I think giving the best solution, as is done here, is the right approach.

|

Code-Apprentice · Accepted Answer · 2012-09-10 13:40:35Z

0

You have two options:

1) Use std::vector instead of an array. This is a very powerful tool and certainly worth learning how to use.

2) Dynamically allocate the array and resize it as you add more items. Basically this means writing your own version of std::vector. This is a good way to strengthen your programming skills. You will learn what goes into writing standard classes and functions. However, I advise using std::vector in more serious programming because it has already been thoroughly tested and debugged.

answered Sep 10, 2012 at 13:40

Code-Apprentice

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