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about logical operator in if!

2 次查看（过去 30 天）
chan
chan 2014-5-25
关闭： MATLAB Answer Bot 2021-8-20
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!

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回答（1 个）

Matt J
Matt J 2014-5-25
编辑：Matt J 2014-5-25
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. "
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Matt J
Matt J 2014-5-26
编辑：Matt J 2014-5-26
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
Matt J 2014-5-26
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

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