đó là bộ sưu tập của RowDefinition và các đối tượng ColumnDefinition, tương ứng, và được quy định cụ thể sử dụng cú pháp yếu tố sở hữu: | CHAPTER 3 CONTROL FLOW CONSTRUCTS action4 You might agree that this looks pretty messy. To make it nicer we can combine the else and the next if into a single word elsif. Here s what the preceding would look like when rephrased in this way if conditionl actionl elsif condition2 action2 elsif conditions actions else action4 Much neater We don t have an awful cascade of closing curly braces at the end and it s easier to see what we re testing and when we re testing it. Let s look at an example. Most of us will not go outside if it s raining but we will always go out for a walk in the snow. We will not go outside if it s less than 18 degrees Celsius. Otherwise we ll probably go out unless we ve got too much work to do. Do we want to go for a walk usr bin perl use warnings use strict print What s the weather like outside Chomp my weather STDIN print How hot is it in degrees chomp my temperature STDIN print And how many emails left to reply to chomp my work STDIN if weather eq snowing print It s snowing let s go n elsif weather eq raining print No way sorry it s raining so I m staying in. n elsif temperature 18 print Too cold for me n elsif work 30 print Sorry - just too busy. n else print Well why not n 62 CHAPTER 3 CONTROL FLOW CONSTRUCTS Let s say it is 201 degrees we ve got 27 e-mails to reply to and it s cloudy out there perl What s the weather like outside cloudy How hot is it in degrees 20 And how many emails left to reply to 27 Well why not Looks like we can fit a walk in after all. The point of this rather silly little program is that once it has gathered the information it needs it runs through a series of tests each of which could cause it to finish. First we check to see if it s snowing if weather eq snowing print It s snowing let s go n If so then we print our message and this is the important part do no more tests. If not we move on to the next test elsif weather eq raining print No way sorry it s raining so I m staying in. n Again if
