How can i do let Matlab returns variable name when i check its value?

Assumed that, i have a code as below:

x=input('x = ');
y=input('y= ');
z=input(z= ');
...and so on.

And my condition is value of any x , y or z... (that user will give into accrossding to keyboard) is must be positive. And i mean is after user give into value of variables above. How can i do to know what variable is negative. For example, I want to my program warning that: " Variable x is negative", My code that i tried. I create a vecto that called "Ktra" and use a for loop.

x=input('x= ');
y=input('y= ');
z=input('z= ');
Ktra=[x y z];
iam = 1;
for i=1:length(Ktra)
    if Ktra(i)<0
        disp('Gia tri nhap can lon hon 0');
        tprintf('So thu tu cua so bi am la: %d \n', iam);
    end
end

Thank you so much!

Answer 1

[Stephen23]

This works for any number of variables, just add them to the cell array V:

V = {'x','y','z'};
S = struct();
for k = 1:numel(V)
    str = sprintf('Please enter %s value: ',V{k});
    tmp = str2double(input(str,'s'));
    if tmp<0
        disp('Gia tri nhap can lon hon 0');
        fprintf('So thu tu cua so bi am la: %s \n',V{k})
    end
    S.(V{k}) = tmp;
end

When run it gives this:

>>
Please enter x value: 23
Please enter y value: 5
Please enter z value: -9
Gia tri nhap can lon hon 0
So thu tu cua so bi am la: z 
>>

and of course the values can be simply accessed using the structure fields:

>> S.x
ans =
    23
>> S.z
ans =
    -9

Note also that I used the faster and more secure option of getting input to return a string: str2double(input(...,'s')), as opposed to the buggy and unpredictable input(...).

[Le Dung]

Thank you so much. it's usefull to me.

But, now. because, here, we have a loop. Assumed that, (for example: x and y).If we have two or more values are negative. So, When program runs, it gives this:

Gia tri nhap can lon hon 0
So thu tu cua so bi am la: x
Gia tri nhap can lon hon 0
So thu tu cua so bi am la: y

I mean, program provides for us two warnings: "Gia tri nhap can lon hon 0".

Of cause, it isn't favourable. So if i only want to one waring for any case. How can i do?

Best Regard!

[Walter Roberson]

V = {'x','y','z'};
S = struct();
gave_warning = false;
for k = 1:numel(V)
    str = sprintf('Please enter %s value: ',V{k});
    tmp = str2double(input(str,'s'));
    if ~gave_warning && any(tmp<0)
        disp('Gia tri nhap can lon hon 0');
        fprintf('So thu tu cua so bi am la: %s \n',V{k});
        gave_warning = true;
    end
    S.(V{k}) = tmp;
end

Answer 2

[Walter Roberson]

Varnames = {'x', 'y', 'z'}

Now you can display Varnames{i}

[Le Dung]

First thank you so much. But, Could you explain more detail? because i'm begineer. thank you so much.