error: ‘mpz_inits’ was not declared in this scope

[Creatxr]

Hi,
It's my first time to use GMP library.
What's happened with this code?
thanks.
=============================================
/main.cpp|11|error: ‘mpz_inits’ was not declared in this scope|
/main.cpp|13|error: ‘mpz_clears’ was not declared in this scope|
=============================================
#include <iostream>
#include <gmp.h>

using namespace std;

void mpz_inverseMod(mpz_t r, mpz_t n, mpz_t m) {
   mpz_t x1, x2, x3;
   mpz_t y1, y2, y3;

   mpz_init(x1);
//-------------------------------------above is correct
   mpz_inits(x1, x2, x3, y1, y2, y3);

   mpz_clears(x1, x2, x3, y1, y2, y3);
}

int main()
{
   cout << "Hello world!" << endl;
   return 0;
}