两个表示复数的字符串
两个数相乘的结果的字符串
1+2i 2+1
0+5i
(1+2i)(2+i) = (2 + i + 4i + 2i * i) = 0 + 5i
1+-2i 3+4i
11+-2i
(1+-2i)(3+4i) = (3 + 4i - 6i - 8i * i) = 11+-2i