将字符串填充到固定长度

string s = "Foo";
string paddedLeft = s.PadLeft(5);        // paddedLeft = "  Foo" (pads with spaces by default)
string paddedRight = s.PadRight(6, '+'); // paddedRight = "Foo+++"
string noPadded = s.PadLeft(2);          // noPadded = "Foo" (original string is never shortened)