Function with return array

[cristinesel]

Hello,
I'm trying create a function that return a array with all ids.
I tried the below code but not worked

#include <iostream>
#include <string>

using namespace std;


string ide()
{
int nanim;
string id[nanim];
cout<<"Enter the number of animals: ";
cin>> nanim;
for (int i=0; i<nanim;i++)
{
cout<< "\nEnter id anim "<<i+1 << "\n";
cin>> id[i];

}
return id;
}

int main()
{

string id = ide();
cout << id <<"\n";
return 0;

}

[vlad from moscow]

This code of course is invalid by several reasons. First of all the return type of function ide is std::string while in the return statement there is array name id that is converted to the pointer to the first element of the array.
Also you should specify a constant expression as the size of an array. In the program variable nanim was not initialized so the next statement has undefined behavior.

int nanim;
 string id[nanim];

In such cases it is better to use std::vector instead of arrays.

[cristinesel]

How can do I rewrite this code for return array? I cant specify a constant expression as the size of an array because I do Know the size...
Thank's

[vlad from moscow]

I would write the function the following way (without testing)

#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 

vector<string> ide()
{
   vector<string> id;
   vector<string>::size_type nanim;

   cout << "Enter the number of animals: ";
   cin >> nanim;
 
   id.reserve( nanim );

   for (  vector<string>::size_type i=0; i < nanim; i++ ) 
   {
      cout<< "\nEnter id anim "<< i+1 << ": "; 

      string s; 
      cin >> s;
      id.push_back( s );
   } 

   return id; 
}
 
int main()
{
   vector<string> id = ide();
   
   for ( const string &s : id )  cout << s <<"\n";

   return 0;
}

[vlad from moscow]

The other way if you are to use arrays is to allocate dynamically memory.

For example

string * ide()
{
   size_t nanim;

   cout << "Enter the number of animals: ";
   cin >> nanim;
 
   string *id = new string[nanim];

   for (  size_t i=0; i < nanim; i++ ) 
   {
      cout<< "\nEnter id anim "<< i+1 << ": "; 

      cin >> id[i];
   } 

   return id; 
}

[cristinesel]

When I do the last code; I cant print all ids, i can print just one id...How can I do to print the array?
I tried:

#include <iostream>
#include <string>
using namespace std;

string * ide(size_t nanim)
{

cout << "Enter the number of animals: ";
cin >> nanim;

string *id = new string[nanim];

for ( size_t i=0; i < nanim; i++ )
{
cout<< "\nEnter id anim "<< i+1 << ": ";

cin >> id[i];


}
return id;
}


int main()
{
size_t n;
string *id =ide(n);
int i=0;
cout << id[i] <<i + 1<< endl;
}

[vlad from moscow]

#include <iostream>
#include <string>
using namespace std;

string * ide(size_t &nanim)
{

cout << "Enter the number of animals: ";
cin >> nanim;

string *id = new string[nanim];

for ( size_t i=0; i < nanim; i++ )
{
cout<< "\nEnter id anim "<< i+1 << ": ";

cin >> id[i];


}
return id;
}


int main()
{
size_t n;
string *id =ide(n);

for ( size_t i = 0; i < n; i++ ) cout << id[i] <<i + 1<< endl;
}

[cristinesel]

ok Thank you!
But I did not want for in the int main..
I tried
#include <iostream>
#include <string>
using namespace std;

string * ide()
{
size_t nanim;
cout << "Enter the number of animals: ";
cin >> nanim;

string *id = new string[nanim];
string *id2 = new string[nanim];

for ( size_t i=0; i < nanim; i++ )
{
cout<< "\nEnter id anim "<< i+1 << ": ";

cin >> id[i];
cout << id[i] <<i + 1<< endl;

}
return id;
}


int main()
{
string *id =ide();
cout << id << "\n";
return 0;
}

But my output was:

Enter the number of animals: 2

Enter id anim 1: 22
221

Enter id anim 2: 333
3332
0xb25ed8

--------------------------------
Process exited with return value 0
Press any key to continue . . .

What is the 0xb25ed8?...

I woud like my id array :22
333

Thank you

[vlad from moscow]

0xb25ed8 is the address of the first element of the array that you are returning from the function.
Also it is not clear why you allocated two arrays.

string *id = new string[nanim];
string *id2 = new string[nanim];

[cristinesel]

I'm sorry
I put the wrong code

string * ide()
{
size_t nanim;
cout << "Enter the number of animals: ";
cin >> nanim;

string *id = new string[nanim];
for ( size_t i=0; i < nanim; i++ )
{
cout<< "\nEnter id anim "<< i+1 << ": ";

cin >> id[i];
cout <<i + 1<< ":"<< id[i] << endl;

}
return id;
}


int main()
{
string *id =ide();
cout << id << "\n";
return 0;
}

[vlad from moscow]

It is not very important for the question that you put a wrong code.
In any case id is a pointer. So line

cout << id << "\n";

displays its value that is the address of the first element of the allocated array.