字符串交叉输入，就是将一个字符串交叉的输入到了另一个字符串当中，比如：

char a[4]="ABCD" char b[4]="abcd"

则char c[8]="AaBbCcDd"

-Cross-string input, is to cross a string input to another string of them, such as:

char a [4] = "ABCD"　char b [4] = "abcd"　

While char c [8] = "AaBbCcDd"