matlab while loop multiple conditions

Question

Hi programming in Matlab here, and for some reason I keep getting errors in my while loop. Can anyone give me an example on how to make multiple conditions in a while loop? Here is my while loop,

while (user_input ~= 256);%try catch does not work very well for this
 prompt = 'Please enter one of the listed gray levels (256, 128, 64, 32, 16, 8, 4, 2). ';
 user_input = input(prompt);
end

I would like it to be something like ,

while (user_input ~= 256 || user_input ~= 128 || user_input ~= 64)

Thank you for your help!

marc_s · Accepted Answer · 2022-10-20 20:13:58Z

2

The symbol & is the and logical operator. You can use it for multiple conditions in your while loop.

while (user_input ~= 256 & user_input ~= 128 & user_input ~= 64)
    prompt = 'Please enter one of the listed gray levels (256, 128, 64, 32, 16, 8, 4, 2). ';
    user_input = input(prompt);
end

As beaker pointed out, what you ask is to ask for input as long as it is not one of the following values : 256, 128 or 64. Using the or logical operator would mean that user_input should be 256, 128 and 64 at the same time to break the loop.

You can also use ismember.

conditional_values = [256, 128 , 64]
while ~ismember(user_input, conditional_values)
    prompt = 'Please enter one of the listed gray levels (256, 128, 64, 32, 16, 8, 4, 2). ';
    user_input = input(prompt);
end

An other way to go, proposed by Luis Mendo, is to use any

conditional_values = [256, 128 , 64]
while ~any(user_input==conditional values)
    prompt = 'Please enter one of the listed gray levels (256, 128, 64, 32, 16, 8, 4, 2). ';
    user_input = input(prompt);
end

user_input == conditional_value returns an array composed of 1s and 0s depending on if values of conditional_values match with user_input. Then any finds if there is at least one 1 on this array. Then we apply ~ which is the not operator.

edited Oct 20, 2022 at 20:13

marc_s

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answered Sep 19, 2015 at 15:49

Ikaros

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6 Comments

Adriaan Over a year ago

I'd go with ismember indeed. +1

beaker Over a year ago

The condition is always satisfied. If user_input == 256 then user_input ~= 128 and user_input ~= 64. I suspect the OP wants &.

Luis Mendo Over a year ago

Or, perhaps simpler, while ~any(user_input==conditional values)

Jon_the_developer Over a year ago

ismemeber seems like the best way since I need something that will act as if it were an ||, not an &&. Thank you for your help.

beaker Over a year ago

@bobdude "I need something that will act as if it were an ||, not an &&"... Not according to your conditions. If you use || you're going to continue looping if your value is not equal to any of the comparison values. You've created an infinite loop since a single value can't be equal to all of them.

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