CareerCup

Sample s[5] = {1,2,3,4,5};

There are multiple ways.
1. Use vector STL.

class A
{
        int p;
        public:
        A(int i)
        {
                p=i;
                cout<<"Called"<<endl;
        }
        A(const A & rhs) :p(rhs.p) {
                cout << "Copied\n";
        }
 
};
 
int main()
{
        vector<A> v(5,A(1));<-------5 objects are constructed.
        return 0;
}

output here: ideone.com/lHX5W

2. Call constructor for each object.
A arr[3]={A(1),A(2),A(3)};
This would be better if we want to initialize different objects with different values.
The first object is initialized with1, second with 2 & so on.

However,in the first method using vector, only one object is constructed & initialized with 1 [in our case], & copy constructor is called 5 times to copy that object.

If you call new, then there will be a constructor call which will search for the default constructor. And, since there is no default constructor and the compiler can't create it because of presence of a parametrized constructor, it will report error.

So, the best you is to allocate the memory C-style and then initialize it.

class A{
public:
int a;
A(int b): a(b){}
};

int main()
{
 A *a1,a2(1);
 a1 = (A*)malloc(sizeof(A)*10); // equivalent to A[10]. 
 for(int i=0;i<10;i++) a1[i]=a2; // Initialization is important in any program.
 for(int i=0;i<10;i++) cout<<a1[i].a;
 return 0;
}

A a[10] = {A(0), A(0), A(0), A(0), A(0), A(0), A(0), A(0), A(0), A(0)};

class TryIt {
	int aa;
	public TryIt(int a) {
		aa=a;
	}
}
public class Misc1 {

	
	public static void main(String [] args) {
		TryIt [] arr ={new TryIt(1),new TryIt(2)};
		
		System.out.println("arr "+arr[0].aa);
	}
}

A a[10] = new A[10];
for( int i=0; i<10; i++)
{
a[i] = new A( i ); // initialized to i;
}

operator new + placement new. Times needed IRL: 0 (use a vector, kids).

Try 2D, like

A **a = new A*[10];
for (int i=0; i< 10; i++) {
a[i] = new A(0);
}

let class A be:
class A{
int a;
public A(int a){
this.a = a;
}
}

so an array of this class can be initialized as:
A[] a = new A[10];

This is not a new question..Sol's got the right one though...from Myers.. :)

B.T.W..comment on Sol's is by Prem.

why this code perfectly running and giving ouput 56

int main()
{
int *p=malloc(0);
*p=56;
printf("%d",*p);
return 0;
}

//Java solution

private A[ ] a;

public A(int i) {
if( a == null) {
System.out.println("executing first time" + i);
a = new A[i];
}
if(i <= 0) {
// done with initialization
} else {
System.out.println("creating object A ..." + i);
a[--i] = new A(i); // creates 'i' number of 'A' objects
}
}

//Java solution

private A[ ] a;

public A(int i) {
if( a == null) {
System.out.println("executing first time" + i);
a = new A[i];
}
if(i <= 0) {
// done with initialization
} else {
System.out.println("creating object A ..." + i);
a[--i] = new A(i); // creates 'i' number of 'A' objects
}
}

//Java solution

private A[ ] a;

public A(int i) {
if( a == null) {
System.out.println("executing first time" + i);
a = new A[i];
}
if(i <= 0) {
// done with initialization
} else {
System.out.println("creating object A ..." + i);
a[--i] = new A(i); // creates 'i' number of 'A' objects
}
}

//Java solution

private A[ ] a;

public A(int i) {
if( a == null) {
System.out.println("executing first time" + i);
a = new A[i];
}
if(i <= 0) {
// done with initialization
} else {
System.out.println("creating object A ..." + i);
a[--i] = new A(i); // creates 'i' number of 'A' objects
}
}

The following solution works :

class B 
{
private :

	int i ;
public :
	
	/*B()
	{
		i = 0 ;
	}*/
	 B(int d)
	{
		i = d ;
		cout<<"const " <<d<<endl;
	}


} ;

int main ()
{
	B b = 1;
	B b1[2]= {1};

	B *ptr[2] = {new B(3) };
    cout << ptr[0]<<endl;
  cout << ptr[1]<<endl;

	return 0;
}

u cannot initialize an array without having a defualt constructor

A a[10] = new A[10]; will give compile error