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in Technique[技术] by (71.8m points)

How to get size c++ dynamic array

I'm studying C++ and I need to create structure Airplane and work with it.

My structure Airplane.h

#include "stdafx.h"
using namespace std;

struct Airplane {
    string destination;
    int number;
    string type;
};

and it's my code

#include "stdafx.h"
#include "Airplane.h"

string SetDestination(int n);
string SetType(int n);
void PrintAirplaneList(Airplane * &airplaneList, int n, string title);
void SortByDestination (Airplane *&airplaneList, int n);
void FindAirplanesAndPrint(Airplane *&airplaneList, int n, string type);

int _tmain(int argc, _TCHAR* argv[])
{
using namespace std;

srand((unsigned)time(NULL));

int n;
cout << "Input n = ";
cin >> n;

Airplane * airplaneList = new Airplane[n];

for (int i = 0; i < n; ++i)
{
    airplaneList[i].destination = SetDestination(rand()%5);
    airplaneList[i].number = rand()%9001 + 1000;
    airplaneList[i].type = SetType(rand()%3);
}

PrintAirplaneList(airplaneList, n, "List:");
SortByDestination (airplaneList, n);
PrintAirplaneList(airplaneList, n, "Sorted list (by destination):");

string type;
cout << "Input type: ";
getline(cin, type);
FindAirplanesAndPrint(airplaneList, n, type);

delete [] airplaneList;

system("PAUSE");
return 0;
}

string SetDestination (int n)
{
    string destination;
    switch(n){
    case 0: destination = "Tokio"; break;
    case 1: destination = "Amsterdam"; break;
    case 2: destination = "Moscow"; break;
    case 3: destination = "Philadelphia"; break;
    case 4: destination = "San Diego"; break;
    default: destination = "Unknown city"; break;
    }
    return destination;
}

string SetType (int n)
{
    string type;
    switch(n){
    case 0: type = "passenger"; break;
    case 1: type = "cargo"; break;
    case 2: type = "post"; break;
    default: type = "unknown type"; break;
    }
    return type;
}

void PrintAirplaneList(Airplane *&airplaneList, int n, string title)
{
    cout << "
";
    cout << title << "

";
    for (int i = 0; i < n; ++i)
    {
        cout << "Destination: " << airplaneList[i].destination << "
";
        cout << "Number: " << airplaneList[i].number << "
";
        cout << "Type: " << airplaneList[i].type << "

";
    }
}

void SortByDestination (Airplane *&airplaneList, int n)
{
    for (int i = 0; i < n - 1; ++i)
    {
        for (int j = 0; j < n -1; ++j)
        {
            if(airplaneList[j + 1].destination > airplaneList[j].destination) continue;
            Airplane tempAirplane = airplaneList[j];
            airplaneList[j] = airplaneList[j + 1];
            airplaneList[j + 1] = tempAirplane;
        }
    }
}

void FindAirplanesAndPrint(Airplane *&airplaneList, int n, string type) {
    cout << "Type - " << type << "
";
    int count = 0;
    for (int i = 0; i < n; ++i)
    {
        if (airplaneList[i].type == type)
        {
            cout << "Destination: " << airplaneList[i].destination << "
";
            cout << "Number: " << airplaneList[i].number << "
";
            ++count;
        }
    }
    if (count == 0)
    {
        cout << "Not found
";
    }
}

I have two questions.
1. I can't input type in

string type;
cout << "Input type: ";
getline(cin, type);
FindAirplanesAndPrint(airplaneList, n, type);

and my function FindAirplanesAndPrint starts to work without any value for type. How to make my programm to get value?
2. How to get size of dynamic array in functions? Because it seems the passing size of array n in every function is the wrong way.

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1 Reply

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by (71.8m points)

"How to get size of dynamic array in functions? Because it seems the passing size of array n in every function is the wrong way."

Yet it is the only way when you use dynamically allocated C-style array.

If you want to avoid sending the size explicitly then pass some object that wraps this raw memory buffer and provides other means of retrieving the size. The most reasonable solution here would be using std::vector<Airplane>.


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