Dynamic Constructor

#include<iostream.h>
#include<conio.h>
#include<string.h>
class A
{
char *nm;
int len;
public:
A()
{
len=0;
nm=new char[len+1];
}
A(char *nm1)
{
len=strlen(nm1);
nm=new char[len+1];
strcpy(nm,nm1);
}
void putA()
{
cout<<"\nName="<<nm;
}
};
int main()
{
char s[20];
clrscr();
cout<<"Enter Name:";
cin>>s;
A a1,a2(s);
a1=a2;
a1.putA();
a2.putA();
getch();
return 0;
}