Program to generate fibonacci series using constructor

#include<iostream.h>
class fib
{
int n;
public:
fib(int a)
{
n = a;
}
fib()
{
n = 0;
}
void display()
{
if(n == 0)
{
cout<"\n No fibonacci number\n";
retun;
}
else if(n == 1)
{
cout<<"Fibonacci numbers are\n"<<"0"<<endl; return; } else if(n>2)
{
cout<<"Fibonacci numbers are\n"<<"0\t1";
}
if f1=0,f2=1,f3,cnt;
for(cnt = 1;cnt <= (n-2);cnt++)
{
f3=f1+f2;
cout<<"\t"<<f3;
f1=f2;
f2=f3;
}
}
};
int main()
{
int a;
cout<<"Enter the series limit:"; cin>>a;
fib f(a);
f.display();
return(0);
}

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OUTPUT
Enter the series limit: 5
Fibonacci numbers are
0 1 1 2 3