數字與字串混合運算的程式

1 + "2" = 12
"1" + 2 = 12
1 + 2 + "3" = 33
1 + 2 + "3" + 4 + 5 = 3345
5 - "3" = 2
"5" - 3 = 2
5 * "3" = 15
"5" * 3 = 15
5 - 2 + "3" = 33
"5" -2 + 3 = 6

參考至： http://tr.ilvs.ilc.edu.tw/~bbfish/learn/javascript/jvar-ex-1.htm