Qfyilyi

I have point(x,y) and i want add another point. i write only formul, but i want getting function:

    struct point {

        mpz_t x;

        mpz_t y;

    };



    point my_func(mpz_t x, mpz_t y) {

   /..../

        //lambda

        mpz_sub(a, Y, y);

        mpz_sub(b, X, x);

        mpz_invert(c, b, P);

        mpz_mul(b, a, c);

        mpz_mod(f, b, P);



        //point x

        mpz_mul(a, f, f);

        mpz_sub(b, a, x);

        mpz_sub(c, b, X);

        mpz_mod(d, c, P);



        //point y

        mpz_sub(a, x, d);

        mpz_mul(b, f, a);

        mpz_sub(c, b, y);

        mpz_mod(e, c, P);



        return (x, y);

    }

It seems to me that this should not be difficult, but I have been driving all day.
point gp = {x, y};
error: array must be initialized with a brace-enclosed initializer

I want only having a point (x, y) to get the next point at the output. it does not have to be a structure, I tried pair and tuple, it still does not help.

really, why bother with something if i need to just change the values ​​of x and y
the void function by reference solved the problem, I am grateful for the useful advice
this function working and need RAM 600kb

void add(mpz_t& x, mpz_t& y, mpz_t& X, mpz_t& Y,  mpz_t& P) {

    mpz_t a, b, c, d, f;

    mpz_inits(a, b, c, d, f, 0);

        //lambda

       mpz_sub(a, Y, y);

       mpz_sub(b, X, x);

    mpz_invert(c, b, P);

       mpz_mul(b, a, c);

       mpz_mod(f, b, P);

        //point x

    mpz_mul(a, f, f);

    mpz_sub(b, a, x);

    mpz_sub(c, b, X);

    mpz_mod(d, c, P);

        //point y

    mpz_sub(a, x, d);

    mpz_mul(b, f, a);

    mpz_sub(c, b, y);

    mpz_mod(f, c, P);

        //set x, y

    mpz_set(x, d);

    mpz_set(y, f);



    mpz_clears(a, b, c, d, f, nullptr);

}