fibonacci c++ gmp generator - c++

Question

Hello I am attempting to implement gmp to an existing fibonacci generator I wrote. I have been reading over the gmp documentation but there is still much I do not understand. The original fibonacci generator is here:
#include <iostream>
using namespace std;
class Fib {
int n;
long unsigned int first, second;
public:
Fib() {
first = 0;
second = 1;
cout << "Enter the number of terms of Fibonacci series you want" << endl;
cin >> n;
cout << "First " << n << " terms of Fibonacci series are:" << endl;
}
int solve() {
int i;
long unsigned int next;
for(i = 0 ; i < n + 1 ; i++) {
if(i <= 1) {
next = i;
}
else {
next = first + second;
first = second;
second = next;
}
}
return next;
}
};
int main() {
Fib fib;
cout << fib.solve() << endl;
return 0;
}
I installed gmp using:
sudo apt-get install libgmp3-dev
When I try to implement gmp I did this:
#include <iostream>
#include <gmpxx.h>
using namespace std;
class Fib {
int n;
mpz_class first, second;
public:
Fib() {
first = 0;
second = 1;
cout << "Enter the number of terms of Fibonacci series you want" << endl;
cin >> n;
cout << "First " << n << " terms of Fibonacci series are:" << endl;
}
int solve() {
int i;
mpz_class next;
for(i = 0 ; i < n + 1 ; i++) {
if(i <= 1) {
next = i;
}
else {
next = first + second;
first = second;
second = next;
}
}
return next;
}
};
int main() {
Fib fib;
cout << fib.solve() << endl;
return 0;
}
I know at some point I need to convert from a int to a string, then clear the output variable or something like that. when I attempt to compile I run:
g++ -lgmpxx -lgmp fib.cpp -o fib
my output:
fib.cpp: In member function ‘int Fib::solve()’:
fib.cpp:30:12: error: cannot convert ‘mpz_class {aka __gmp_expr<__mpz_struct [1], __mpz_struct [1]>}’ to ‘int’ in return
return next;
^
I am a complete noob to bignum libraries, any help would be great. I am reading the documentation but I am struggling with implementing it.

Answer 1

Solved, thank you Marc Glisse for pointing me in the right direction!
I simply removed the function return and allowed the function to just return the ouput.
#include <iostream>
#include <gmpxx.h>
using namespace std;
class Fib {
int n;
public:
Fib() {
cout << "Enter the number of terms of Fibonacci series you want" << endl;
cin >> n;
cout << "The " << n << "'st Fibonacci number is:" << endl;
}
void solve() {
int i;
mpz_class first, second, next;
first = 0;
second = 1;
for(i = 0 ; i < n + 1 ; i++) {
if(i <= 1) {
next = i;
}
else {
next = first + second;
first = second;
second = next;
}
}
cout << next << endl;
}
};
int main() {
Fib fib;
fib.solve();
return 0;
}
output:
Enter the number of terms of Fibonacci series you want
3301
First 3301 terms of Fibonacci series are:
330153163507162264637094778670152653434758914922281728912670042596222213549775330156165336158736310556035302724174567603559968964146698655928480718496410717009709564103992213321320869628734803460669663152332798570186240768164370808688660485835985642189726235311578136722218902035069558368032277843436948382319806290480685283349217035498351102885889468646619750569482644246863804467015344937199892515242806415403581786532923017170033416624774209919795051514102027827396052441847160310846646083321110222356075543424672128051593137886359425865994528848747739182600228659941846983982384323813903695048726976986370288741982958687841091743740983161275336114608885705665822704734020694899622487801
ubuntu#ubuntu:~/projects/c++/fibonacci_cpp$