Matlab User Input/While Loop

Question

I'm writing a function in Matlab that prompts the user to select an Instrument (.wav file) to be read in using the wavread function.

I'm trying to include some sort of error handling/deal with incorrect inputs from the user.

So far my function looks like this:

prompt = 'Select Instrument, Piano: [P], Fork: [F], Violin: [V], Gameboy: [G]';
str = input(prompt,'s');
if isempty(str)
    str = 't';
end

while(str ~= 'P') || (str ~= 'F') || (str ~= 'V') || (str ~= 'G')
    prompt = 'Invalid Selection! Choose, Piano: [P], Fork: [F], Violin: [V], Gameboy: [G]';
    str = input(prompt,'s');
    if isempty(str)
        str = 't';
    elseif (str == 'P') || (str == 'F') || (str == 'V') || (str == 'G')
        break
    end
end

If prompted during the while loop, it successfully prompts the user and reads in the .wav, but if the user presses P,F,V, or G on the first prompt, the while loop is still used and "Invalid Sel... " is still displayed...

I'm not sure how I should be implementing this....

Samuel Colvin · Accepted Answer · 2013-04-10 12:41:03Z

3

that's because you logic is wrong

(str ~= 'P') || (str ~= 'F') || (str ~= 'V') || (str ~= 'G')

is always true as str is always going to be different from either P, F, V or G. It can't be the same as all of them which is what you are asking.

It should be

str ~= 'P' && str ~= 'F' && str ~= 'V' && str ~= 'G'

or

~(str == 'P' || str == 'F' || str == 'V' || str == 'G')

or in sane matlab

~any('PFVG' == str)

answered Apr 10, 2013 at 12:41

Samuel Colvin

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1 Comment

Reanimation Over a year ago

Oh of course. I feel silly now. Thanks for clearing that up. Problem solved :D Also ~any('PFVG' == str) is a really cool line of code, I'm going to use this. Thanks for your time.

Ne_Plus_Ultra · Accepted Answer · 2013-04-10 12:43:51Z

1

how about using strcmp?

str = input(prompt,'s');
if isempty(str)
    str = 't';
end

while ~any(strcmp(str,{'P' 'F' 'V' 'G'})) %|| (str ~= 'F') || (str ~= 'V') || (str ~= 'G')
    prompt = 'Invalid Selection! Choose, Piano: [P], Fork: [F], Violin: [V], Gameboy: [G]';
    str = input(prompt,'s');
    if isempty(str)
        str = 't';
    elseif (str == 'P') || (str == 'F') || (str == 'V') || (str == 'G')
        break
    end
end

answered Apr 10, 2013 at 12:43

Ne_Plus_Ultra

1912 silver badges15 bronze badges

1 Comment

Reanimation Over a year ago

I've not seen the strcmp before. I'm going to have a read up of it now. Thanks for you time :D

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