How to write switch statement

For an assignment i am supposed to convert this if else statement into a switch case statement:

if val > 5
   if val < 7
     disp('ok(val)')
   elseif val < 9
        disp('xx(val)')
   else
        disp('yy(val)')
   end
else
   if val < 3
     disp('yy(val)')
   elseif val == 3
        disp('tt(val)')
   else
        disp('mid(val)')
   end
end

Currently I have this, however it does not display anything when assign val any number, except 1:

switch val 
    case val < 3
        disp('yy(val)')
    case val == 3
        disp('tt(val)')
    case 3 < val <= 5
        disp('mid(val)')
    case 5 < val < 7
        disp('ok(val)')
    case 7 <= val < 9
        disp('xx(val)')
    case 9 < val
        disp('yy(val)')
end

Answer 1

[Cris LaPierre]

Your syntax for the logical comparison is incorrect. You can't perform 2 comparisons on the same item. You must split this into 2 conditional statements.

% incorrect 
case 3 < val <= 5
    
% Correct
 case 3 < val && val <= 5

The next thing to realize is that a switch statement looks for the case that matches the value you are switching on. This means your switch val has to match an actual value listed in a case statement. You case statements all perform logical comparicsons, so their value is true or false (1 or 0). If val is ever anything other than 1, it can't find a match.

You are looking for the true case, so use switch true.

[Walter Roberson]

"You can't perform 2 comparisons on the same item" is not completely correct, with the exception being in the processing of piecewise() involving symbolic expressions.

syms x
f(x) = piecewise(x < 2, 1, 2 <= x < 3, 2, 3)

f(x) = 

fplot(f, [0 4])

But notice:

g(x) = 2 <= x < 3

g(x) = 

does not do the same thing: it is only piecewise() that handles chained tests.

Answer 2

[Walter Roberson]

You can use the obscure

switch true

However you will need to fix your chains of conditions. In MATLAB,

    3 < val <= 5

is

    ((3 < val) <= 5)

The first part is evaluated and returns 0 (false) or 1 (true), and you then compare the 0 or 1 to 5...