about logical operator in if!

This is my code

y = input('choose','s');

if y == 'a1' | y == '1a'

      disp('win')
  else
      disp('lost')
  end

I would like to ask that when I use this, while I am run this program, I type only a or only 1 it also display win, like i type 1a or a1 . explain to me, or me have other ways to write the code, I do not need to add elseif more.

Thanks!

Answer 1

[Matt J]

Use strcmp()

if strcmp(y,'a1') || strcmp(y,'1a')
      disp('win')
  else
      disp('lost')
  end

As for understanding what's happening currently, observe the result of each of your sub-expressions, and the vectors of logical data they produce, when y='1',

>> y='1';

>> y == 'a1'

ans =

       0     1

>> y == '1a'

ans =

       1     0

>> y == 'a1' | y == '1a'

ans =

       1     1

Since (y == 'a1' | y == '1a') produces a vector of trues, the whole if statement evaluates to true. As mentioned in "doc if",

" An evaluated expression is true when the result is nonemptyand contains all nonzero elements (logical or real numeric). Otherwise,the expression is false. "

[Matt J]

You could also use ismember

 if  ismember(y,{'a1','1a'})
      disp('win')
  else
      disp('lost')
  end

[Matt J]

chan Commented:

Thanks for the good, answer, so mean we cannot use the simple condition, right? y == 'a1' | y == 'a1'

[Jos (10584)]

to see if two things are equal use isequal, rather than ==

isequal(y,'a1')

For character arrays (strings) A and B, you can use strcmp(A,B)

For numerical arrays A and B (of the same length!), you may use all(A==B)

[Matt J]

to see if two things are equal use isequal, ... isequal(y,'a1')

Be careful when using isequal to compare strings. It doesn't check that both arguments are class char, e.g.,

    >> isequal(':',58)

    ans =

         1

whereas,

    >> strcmp(':',58)

    ans =

         0

[Matt J]

so mean we cannot use the simple condition, right? y == 'a1' | y == 'a1'

You can use these kinds of comparisons when they are appropriate to what you are doing. For example, suppose I want to remove all the spaces in a string,

    >> y='This is a short string'; y(y==' ')=''

    y =

    Thisisashortstring