Weird problem with rand() and object

[Veneficus]

Hello everyone,

I am having a problem with following code. When I try to access the data member "i" in the Numbers class from the main() it prints "-858993460". But in the constructor it assigns and prints a random number without a problem. I am pulling my hair out since I couldn't figure out what I am doing wrong. I appreciate it if you can land me a hand and tell me what's wrong.

Oh by the way I tried with an accessor function and got the same result.

Thanks,

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#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <ctime>
using namespace std;


class Numbers {
public:
int i;
Numbers (int i = 0);
};

Numbers::Numbers (int i)
{
i = rand ();
cout << i << endl;
}



int main (void)
{
srand (time (NULL));
Numbers myNumbers;
cout << myNumbers.i << endl;
return 0;
}
---------------------------------------------------------------------------------



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[PerFnurt]

You assign the wrong i.

class Numbers {
public:
int i; // <== This i is the one you print in main, but you never assign it any value
Numbers (int i = 0);
};

Numbers::Numbers (int i) // <=== This is i is assigned...
{
i = rand (); // ...with a random number
cout << i << endl;
}

 

[Zyrenthian]

perfnurt is correct but here is a bit more clarification. Because the parameter to Numbers is also called &quot;i&quot;, when you get into the constructor, you are not accessing your member variable i but the local variable to the constructor, declared in its parameters. If you change the variable name, it will work fine. Also, use of the this pointer would work.

ex:

Numbers::Numbers(int local_i)
{
i = rand();
cout<<i<<endl;
}

However, I dont see a reason to have a value in the constructor. I would suggest, unless there is a reason, to do the following

class Numbers
{
public:

// int i; dont call it i... it can get confusing
int m_randomNumber;

Numbers();
Numbers(int rand_value);
};

Numbers::Numbers()
{
m_randomNumber = rand();
cout<<m_randomNumber<<endl;
}

Numbers::Numbers(int rand_value):m_randomNumber(rand_value)
{}

// On a side note your original constructor would work if you did

Numbers::Numbers(int i)
{
this->i = rand();
cout<<this->i<<endl;
}

Matt

 

[Veneficus]

Thanks a lot Zyrenthian and PerFnurt. I knew I was doing something stupid.

Well with the light of your help I've changed the class definition to following:

class Numbers {
public:
int i;
Numbers (void) {i=rand();}
friend void fill_class (Numbers &);
};

Thanks a lot.