complex solution

#include <stdio.h>
#include <math.h>

typedef struct {
    double re, im;
} Complex;

int main(void) {
    Complex z;
    int retry = 1;
    do {
        --retry;
        Complex z0;
        printf("初期値のRe:"); scanf_s("%lf", &z0.re);
        printf("初期値のIm:"); scanf_s("%lf", &z0.im);
        int i = 0;
        double a = 0.00001;
        do {
            i++;
            z.re = z0.re;
            z.im = z0.re;
            double f_re = z0.re * z0.re - z0.im * z0.im + 5 * z0.re + 7;
            double f_im = 2 * z0.re * z0.im + 5 * z0.im;
            double df_re = 2 * z0.re + 5;
            double df_im = 2 * z0.im;
            double denom = df_re * df_re + df_im * df_im;
            z0.re = z0.re - (f_re * df_re + f_im * df_im) / denom;
            z0.im = z0.im - (- f_re * df_im + f_im * df_re) / denom;
        } while (fabs(z.re - z0.re) > a && fabs(z.im - z0.im) > a);
        z.re = z0.re;
        z.im = z0.im;

        printf("Re=%f , Im=%f, 回数は%d\n", z.re, z.im, i);

        puts("続けるなら0を");
        scanf_s("%d", &retry);
    } while (retry > 0);
}