https://pintia.cn/problem-sets/12/problems/348
1 struct complex multiply(struct complex x, struct complex y) 2 { 3 struct complex ret; 4 5 ret.real = x.real * y.real - x.imag * y.imag; 6 ret.imag = x.real * y.imag + x.imag * y.real; 7 8 return ret; 9 }