File Exchange Pick of the Week
January 2nd, 2008
MATLAB Basics: ‘Switch case’ vs. ‘If elseif’
This three minute video takes a look at the “Switch case” flow control statement and contrasts it with the more familiar “If elseif” flow control statement.
Often times, people will use an “If elseif” statement where a “Switch case” statement is going to be cleaner and easier to understand and maintain.
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Find the files here.
PodCast here
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Other MATLAB Basics posts have been gathered here:
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As a cool little post script: At most places you celebrate the 100th something or other, but since this is a software company I feel I should celebrate the 64th video (2^6) and as I post this I see that it is the 18128th file on the File Exchange capturing the next power of two in the last three digits.
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Ok thanks Doug for this, but which of if-else and switch-case is computationally more efficient??
Robert,
I tested, and it really depended on the number of iterations. For reasonable numbers of iterations it did not seem to matter. TIC TOC and the profiler can be a big help here.
When asked about these kinds of things, I often say “Just code it”, run the profiler and see where the problems are. There is no need to try and optimize one second off of this kind of statement when there is some calculation that take 300 seconds anyways. Write your code clean and maintainable, then modify the slow bits as they appear.
Doug
Doug,
I often see programmers rely on the ‘if elseif’ chain in order to determine if a variable (n) falls into one of several ranges. MATLAB help is not clear on how this is done using the switch statement, but it is possible by comparing the logical value true against each of the range evaluations…
n=80
switch logical(true)
case n>100, disp(’high’);
case n>50, disp(’moderate’);
case n>0, disp(’low’);
otherwise disp(’invalid’);
end;
Again, this is a much more elegant solution than the ‘if elseif’ alternative.
Phil.
Phil,
Excellent example. Thank you!
Doug
Phil,
Thanks for that! Exactly what I was looking for. MATLAB help does kind of fail to explain how to use logicals with a switch statement.
Jon
I want to use the switch/case for the following. I want to prompt the user to input one the following strings: triangle, square,pentagon or hexagon. Depending which figure you input the program will then calculate the sum of the interior angles of the figure using (n-2)(180). I tried the following and I’m prompted with an error message. Here is my code.
clear;
clc;
n=input(’Please input the figure:’)
switch n
case (’triangle’)
n=3;
sum=(n-3).*(180)
case (’square’)
n=4;
sum=(n-3).*(180)
case(’pentagon’)
n=5;
sum=(n-3).*(180)
case (’hexagon’)
n=6;
sum=(n-3).*(180)
end
Please could you assist me.
Thanks
Phillip,
You need this for your input statement:
n=input(’Please input the figure:’,’s’)
This interprets whatever is typed as a string. Without that switch, MATLAB is taking what you type and interpreting it and thus looks for a function called “triangle” or whatever and does not find it.
Doug
Doug,
I’m looking for a GoTo function for Matlab. I have an efficient search routine that I like to use in a number of areas that requires GoTos. Is there anything like this in matlab procedures?
Thank you for your help,
Rick
Never Mind, I found a more efficient way to do it. Instead of searching the time area I simply multiply the time by the delta time to acquire the index number in the array. Thanks for your web tutorials. They are very helpful.