what is wrong in this code?

If you aim to program in C++ (in contrast to C), you should use C++ means. Especially, C++ has various containers that abstract from explicit memory management. A possible solution could be:

#include <vector>
#include <string>
#include <iostream>

using namespace std;

int main(void)
{
    vector<string> names;
    while(true) {
        cout << "Please enter a name (a dot ends asking for names): ";
        string name;
        cin >> name;
        if (name == ".") break;
        names.push_back(name);
    }
    for(auto it = names.begin(); it != names.end(); ++it) {
        cout << "Name: " << *it << endl;
    }
    return 0;
}

Cheers
Andi

In the second loop you need to define a variable "i" like this, it is not defined in this scope :

//for( i=0;i<5;i++)
for(int i=0;i<5;i++)
{
    cout<<a[i];
}

Obviously, your own code is like a blackbox to you. It don't do what you expect.
What follow is not directly a solution to your problem, but a key that will help you to understand by yourself what is wrong.
The debugger is your friend. It will show you what your code is really doing.
Follow the execution, check variables and you will see that there is a point where it stop doing what you expect.

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]

//Try this... it should work in most c or c++ compilers

#include <stdio.h>
void main()
{
    char a[100]; //buffer for 5 names of 20 chars max
                     //must insure no over run not implemented
    for (int i=0;i<5;i++)
    {
        printf("Enter a name[%i]=",i); //print a prompt
        gets(&a[i*20]);  //get the name
        //printf("\n");  //might be needed to make input on a newe line
    }
    for (i=0;i<5;i++)
        printf("Name[%i]=%s\n",i,&a[i*20]); //print name
    getchar();
}

//here is another method using C++ will not compile in a C compiler
//but it is safer to use since it utilizes the C++ std::string class
//and thus the user can type any length names without the risk of overwriting
//memory

#include <stdio.h>
#include <string>
#include <iostream>
using namespace std;
void main()
{
	string a[5];
	for (int i=0;i<5;i++)
	{
	    printf("Enter a name[%i]=",i); //print a prompt
	    cin >> a[i]; //get name
	}
	for (i=0;i<5;i++)
	    cout << "name[" << i << "]=" << a[i] << "\n"; //print names
    getchar();
}