works in debugger mode. Crashes in executable mode - c++

Question

The code was written in VS community 2013. The program worked fine in debugger mode. But crashed while execution. Please let me know what could be the problem.
sample test case:
10
aaa
bbb
ccc
aaa
The program crashed at 3rd input line, sometimes at 4th input line.
#include<iostream>
#include<string.h>
#include<string>
using namespace std;
class registeration
{
public:
char* name;
int count;
registeration *next;
registeration()
{
name = new char(20);
count = 0;
next = NULL;
}
};
int main()
{
int n;
cin >> n;
char* str = new char(n);
registeration *regStart = new registeration();
while (n--)
{
cin >> str;
if (regStart->next == NULL)
{
registeration *reg = new registeration();
regStart->next = reg;
reg->count++;
//strcpy(reg->name, str);
strcpy_s(reg->name, 20, str);
}
else
{
registeration *reg = new registeration();
reg = regStart->next;
while (reg->next != NULL && strcmp(str, reg->name))
{
//registeration *reg1 = new registeration();
reg = reg->next;
}
if (!strcmp(str, reg->name))
reg->count++;
else
{
registeration *reg1 = new registeration();
strcpy_s(reg1->name, 20, str);
reg1->count++;
reg->next = reg1;
}
}
}
registeration *reg = new registeration();
reg = regStart->next;
while (reg != NULL)
{
if (reg->count > 1)
cout << reg->name << endl;
reg = reg->next;
}
return 0;
}

Answer 1

One obvious bug is in these lines:
name = new char(20);
char* str = new char(n);
They allocate a single character initialized to the given value. Instead you intend to allocate an array of characters, which you do as follows:
name = new char[20];
char* str = new char[n];
(With bracket instead of parentheses.)
It is better though to use the standard C++ utilities that manage the memory for you, like std::string for strings and std::vector or std::list for the containers.
EDIT: This code does the same thing as yours, better:
#include <iostream>
#include <string>
#include <map>
using namespace std;
int main()
{
int n;
cin >> n;
map<string, int> m;
for(int i = 0; i < n; ++i)
{
string s;
cin >> s;
m[s]++;
}
for(const auto &pr : m)
if(pr.second > 1)
cout << pr.first << '\n';
}