#include<stdio.h>

typedef struct
{
     double real;
     double imm;
} Complex;

Complex product(Complex c1, Complex c2)
{
      Complex result;

      result.real = c1.real * c2.real - c1.imm * c2.imm;
      result.imm = c1.real * c2.imm + c1.imm * c2.real;

     return result;
}

void print_complex(Complex c)
{
      printf("%d + %di", c.real, c.imm);
}

int main()
{
     Complex c1, c2, c3;

     c1.real = 4;
     c1.imm = 5; // 4 + 5i

     // ...
     // c2 = 8 + 6i
     // c3 = 0

     Complex nums[] = {c1, c2, c3};

     Complex prod;
     prod.real = 1;
     prod.imm = 0;

     for (int i = 0; i < 3; i++)
           prod = product(prod, nums[i]);

     print_complex(prod); // dovrebbe essere 0 + 0i

     return 0;
}