I got a value followed by a program, I want to print some message by using switch statement. I wrote some code , but wrong case is working.

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sam CP 2018-6-25

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编辑： sam CP 2018-6-27

If my result is between 22 and 34 then i have to print "red", result is between 34 and 67 then message should "green", otherwise "blue". I wrote following code.When my result=27 then it will print 'blue', it will always print 'blue. I knew that this will always work on 'otherwise'. How can i solve this?

if true
   switch (n) 
    case (22<n)&&(n<33)
        disp('red')
    case (33<n)&&(n<67)
        disp('green')
    otherwise
        disp('blue')

end

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Answer 1

Adam Danz 2018-6-25

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编辑：Adam Danz 2018-6-25

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It looks like you're mixing up switch/case and logical conditionals. Each case in your example should be a possible outcome of 'n'. If n=23, when you evaluate your first case, (22<n)&&(n<33) = true (=1). But the switch/case is looking for 23. Since none of your cases match 23, it always ends up in 'otherwise'.

In your example, get rid of the switch/case and replace it with conditionals.

if (22<n)&&(n<33)
    disp('red')
elseif(33<n)&&(n<67)
    disp('green')
else
    disp('blue')
end

If n could equal 22, 33, or 67 you might want to use <= rather than <.

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sam CP 2018-6-25

编辑：sam CP 2018-6-25

But i have to implement 8 conditions ...Not 3 conditions

Adam Danz 2018-6-25

The if/then example consumes the same number of lines as a switch/case syntax would. The simplest form would be to use @Guillaume's example which uses discretize().

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Answer 2

Guillaume 2018-6-25

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You are inventing your own syntax for switch, it's no wonder it doesn't work.

While there is a way to make your tests work with switch it would be a very obscure syntax that would confuse many people. So I would recommend not to use it. Instead use if ... elseif ...:

if n >= 22 & n < 33
   disp('red');
elseif n >= 33 & n < 67
    disp('green');
elseif n >= 67 & n < 100
    disp('blue');
else
    disp('purple');
end

Notice that I have changed some of the comparisons to >= as in your original code, if n was exactly equal to an edge value, it would never match anything.

However, your case attempt and the above is a lot of work which can be easily replaced by just two lines using discretize

outputs = {'', 'red', 'green', 'blue', 'purple'};  %the '' is for values less than 22
disp(outputs{discretize(n, [-Inf, 22, 33, 67, 100, Inf])});

It's also trivial to add new outputs/thresholds with this.

Now, if you really really want to use switch:

%WARNING: OBSCURE SYNTAX. DO NOT USE
switch true
  case n >= 22 & n < 33
      disp('red');
  case n >= 33 & n < 67
      disp('green');
  case n >= 67 & n < 100
      disp('blue');
  otherwise
      disp('purple');
end