MATLAB: Using if, else-if and else

if/elseif/else

Hi i am trying to figure out how i can use if, elseif and else to find the first value in an array to fall below the value 5, any help understanding how this can be done would be appreciated.

thanks

Best Answer

If I get it right, you have an array and you want to find its first value (index-wise) less than 5. If this is the case, and there is no particular reason forcing you to use "if", "then" and "else", then you can achieve this very easily. Assuming that your vector is called v, the index of the element you are looking for is

 i = min(find(v<5));

Note that if all the elements of v are >= 5, the instruction

 find(v<5)

will output an empty vector "[]", and the same will do the "min" function. Therefore, you'll get

 i = []

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MATLAB: User input if, else if statement

You need a "==" instead of "=" for comparing values. Here are some other comments:

info = menu('More information?', 'Yes', 'No');
if info == 1
    open Results1.txt;
    pause; %probably should put a break / pause / return here to prevent script from running.
elseif info == 2
    fprintf('script will run\n'); %added \n to ensure next print statement is on next line.
    %continue; %is this inside a for/while loop? Then continue works. Otherwise, continue not needed.
end

MATLAB: Help with if, else if & else statements

You are using else if as if it was elseif

That is,

if condition1
    action1
else if condition2
        action2
end

is not valid. Valid would be

if condition1
    action1
else if condition2
        action2
end
end

which is equivalent to

if condition1
    action1
else
    if condition2
        action2
     end
end

Also legal is

if condition1
    action1
elseif condition2
    action2
end

Notice there is only a single end

You are probably wondering what the difference is between them. Well suppose you had

r = rand;
if r <= 1/2
    disp('first half')
else if r <= 3/4
        disp('third quarter')
end
disp('another message')
end

Then when we space it better, we get

r = rand;
if r <= 1/2
    disp('first half')
else
    if r <= 3/4
        disp('third quarter')
    end
    disp('another message')
end

and you can see that 'another message' sent out as long as r <= 1/2 is false, including if r <= 3/4 is ture. But if we had

r = rand;
if r <= 1/2
    disp('first half')
elseif r <= 3/4
        disp('third quarter')
end
disp('another message')

then "another message" is always sent out.

Best Answer

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MATLAB: Help with if, else if & else statements

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