|
|
相关文章推荐
Sie verfolgen jetzt diese Frage
i think in matlab there is no difference between switch and many if/elseif statements. the switch is also known in many other programming languages, but behaves a bit differently than in matlab. in matlab the corresponding case is executed and the code continues behind the block, in other languages the switch block is exited only if there is a break at the end of the case, otherwise other cases would be tested too. i hope i remebered correctly, it has been some time since my last c++ session
https://de.mathworks.com/matlabcentral/answers/809260-difference-between-switch-and-if#answer_681245
https://de.mathworks.com/matlabcentral/answers/809260-difference-between-switch-and-if#answer_681245
if/elseif/else
is quite similar to
switch/case/otherwise
. Both provide a default action when no conditions are met (
else & otherwise
) and you're encouraged to use those options. In Matlab, both sets of tests stop execution once a condition is met (in some other languages all cases are executed when there are multiple case matches). I doubt either approach has a computationally efficient beneifit over the other.
Here are some of their differences.
- When there are multple conditions, switch/case/otherwise is often the more organized approach resulting in more readable code. It often reduces the need to use operators and functions to test each condition. For example, when testing string matches, if/elseif/else requires using a string comparson function such as strcmp/i , ismember , etc or an operator ( == ) for strings while a switch/case/otherwise just uses a string for each case and if case sensitivity should be ignored, the switch statement could use upper/lower to force the sting to upper or lower case while each case-condition contains the same letter-case.
- switch/case/otherwise is easier to lay out when conditions all rely on the same class such as testing matches to strings, categories,enumerated values but if/elseif/else can be easier to write and read with mixed classes or complex condition tests such as ranges of values. Note that both sets of tests can use expressions or call functions in Matlab but it can become unpleasent to design and read using switch/case/otherwise .
Which is more readable for you (ignore that these can likely be vectorized)?
% Example 1
country =
'Croatia'
;
switch
lower(country)
case
'albania'
y =
...
case
'bosnia'
y =
...
case
'croatia'
y =
...
case
'slovenia'
y =
...
otherwise
error(
'Country not listed: %s'
, country)
end
if
strcmpi(country,
'Albania'
)
y =
...
elseif
strcmpi(country,
'Bosnia'
)
y =
...
elseif
strcmpi(country,
'Croatia'
)
y =
...
elseif
strcmpi(country,
'Slovenia'
)
y =
...
else
error(
'Country not listed: %s'
, country)
end
x = pi;
switch
true
case
x>0 && x<=1
y =
...
case
x>1 && x<=2
y =
...
case
x>2 && x<=3
y =
...
case
x>3 && x<=4
y =
...
otherwise
y = . . .
end
if
x>0 && x<=1
y =
...
elseif
x>1 && x<=2
y =
...
elseif
x>2 && x<=3
y =
...
elseif
x>3 && x<=4
y =
...
else
y = . . .
end
Also see
https://de.mathworks.com/matlabcentral/answers/809260-difference-between-switch-and-if#answer_681270
https://de.mathworks.com/matlabcentral/answers/809260-difference-between-switch-and-if#answer_681270
They're pretty much the same, just slightly different syntax as to how to get the condition. Switch requires an extra line of code than if but that's no big deal.
switch
(value)
case
1
% code
otherwise
% code
end
% 4 lines of code
if
value == 1
% code
else
%code
end
% 3 lines of code
Use which ever one you think makes it easier to read your code. If the condition needs to be made up from multiple tests/operations, then it might be better in an if. switch is best for situations where the condition is just a single value (number, string), or cell array of several such values.
value = (blah + fubar) * snafu
switch
(value)
case
1
% code
case
{2, 3}
% code
otherwise
% code
end
if
(blah + fubar) * snafu == 1
% code
elseif
(blah + fubar) * snafu == 2 && (someOtherVariable == 3)
% Hard to do with "case"
% code
end
My two cents worth, for what it's worth.
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
推荐文章