Error check if statement

Hi all,

I am trying to create a program to calculate resistor values from the colour code. The calculations work but I tried to input an error checking step to ensure that only valid colours are input by the user. For some reason it dosen't work as I expected. I have defined the values of the resistors at the beginning as individual variables then tried to create an if statement that would check that only a valid colour is input later on. Can anyone see where I went wrong??

Thanks

black = 0;
brown = 1;
red = 2;
orange = 3;
yellow = 4;
green = 5;
blue = 6;
violet = 7;
grey = 8;
white = 9;
gold = 5;
silver = 10;

%Request number of bands on the resistor from User
x=input('No of bands = ');
% If 4 BAND resistor use following code block
if x==4
    %Input colours of each band of the resistor
    k = input('band 1 colour = ');
    l = input('band 2 colour = ');
    m = input('band 3 colour = ');
    n = input('band 4 colour = ');

      if k ~= black||brown||red||orange||yellow||green||blue||violet||grey||white
          disp('Incorrect Colour for Band 1')
      elseif l ~= black||brown||red||orange||yellow||green||blue||violet||grey||white
          disp('Incorrect Colour for Band 2')
      elseif m ~= black||brown||red||orange||yellow||green||blue||violet||grey||white||gold||silver
          disp('Incorrect Colour for Band 3')
      elseif n ~= brown||red||gold||silver
          disp('Incorrect Colour for Band 4')
      else
      end 

      o = k*10 + l;
      p = o * 10^m;

      disp ('resistor value (ohms) = '); disp(p); 

         if n == red||brown||gold||silver
         disp('tolerence (+/-) % = '); disp(n);
     else
         disp('incorrect input')
         end

Answer 1

[Star Strider]

I would replace your tests with this ‘test’ function and calls to it.

Example:

test = @(k) ismember(k,{'black','brown','red','orange','yellow','green','blue','violet','grey','white'});

k = 'red'
Out1 = test(k)
k = 'indigo'
Out2 = test(k)

k =
red

Out1 =
     1

k =
indigo

Out2 =
     0

That should also make your code more efficient.

Answer 2

[Walter Roberson]

k ~= black||brown||red||orange||yellow||green||blue||violet||grey||white

means the same thing as

(k ~= black) || (brown ~= 0) || (red ~= 0) || (orange ~= 0) || (yellow ~= 0) || (green ~= 0) || (blue ~= 0) || (violet ~= 0) || (grey ~= 0) || (white ~= 0)

which is of course always true since brown ~= 0

I have been unsuccessful in finding any computer languages which "distribute" relational operators in the way you thought MATLAB worked, so I have yet to figure out where people are picking up the idea that it could work.

I suggest that you consider using ismember()