cannot do substraction in mpir

Question

I am new to programming and I have a coding homework. We have to implement RSA using MPIR. I generated p and q the best way I could think of. I could not make them 512 bits, but I will continue as it is. I also did not test for primality yet. I will deal with the byte size and primality test if I have time.

My problem is regarding finding Phi(n) = (p-1)*(q-1). I manage to find p, q and N, but Phi(n) and N give the same result. I checked the functions in the MPIR document multiple times and I tried two similar functions for substraction as you will see, but still no luck. (I did not write the code for q here as it is a repetition of p.)

Can someone guide me? I would like to say thank you in advance.

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <mpir.h>
#include <cstdlib> 
#include <iostream>

using std::cout;
using std::cin;


   int main()
   {

    mpz_t p;
    mpz_init(p); 

    mpz_t randint;
    mpz_init(randint);

    gmp_randstate_t state;
    gmp_randinit_mt(state);

    mpir_ui seed;


    cout << "Please choose a number for the seed of the random number 
    generator:";
    cin >> seed;

    gmp_randseed_ui(state, seed);
    mpz_urandomb(randint, state, 512); 

    mpz_t limit;
    mpz_init(limit);
    mpz_t winner;
    mpz_init(winner);


    mpz_ui_pow_ui(limit, 2, 511);

    mpz_ior(winner, limit, randint);

    mpz_next_prime_candidate(p, winner, state);

    gmp_randclear(state);
    mpz_clear(randint);
    mpz_clear(winner);

    mpz_t q;
    mpz_init(q);

    mpz_init(randint);
    gmp_randinit_mt(state);

    cout << "Please choose a number for the seed for the random number 
    generator :";
    cin >> seed;


    gmp_randseed_ui(state, seed);
    mpz_urandomb(randint, state, 512);


    mpz_init(limit);

    mpz_init(winner);

    mpz_ui_pow_ui(limit, 2, 511);

    mpz_ior(winner, limit, randint);

    mpz_next_prime_candidate(q, winner, state);

    gmp_randclear(state);
    mpz_clear(randint); 
    mpz_clear(limit);
    mpz_clear(winner);


   // Now we find n=p*q
 
    mpz_t N; 
    mpz_init(N);

    mpz_mul(N, p, q);


    mpz_t phin;
    mpz_init(phin);


    mpz_t pa;
    mpz_init(pa);
    mpz_t qa;
    mpz_init(qa);

1st way

    mpz_t one;
    mpz_init(one);
    mpz_set_ui(one, 1);


    mpz_sub(pa, p, one); 
    mpz_sub(qa, q, one);

    mpz_mul(phin, pa, qa);

Second way

    mpz_sub_ui(pa, p, 1); 
    mpz_sub_ui(qa, q, 1);

    mpz_mul(phin, pa, qa);

Then I write them to a document and clear everything.