problem with if statment

Question

huda nawaf 2011-8-20

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/14115-problem-with-if-statment

hi,

I write very simple code

x=dec2bin(1024);

 for i=1:11
     if x(i)== 0 
         i
              end
end
when I ran it , I don't know why it not meet the condition , then print i.
this code is part from a long code that relate my work.
thanks

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Answer 1

Arturo Moncada-Torres 2011-8-20

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The problem is that dec2bin returns the binary number in a string and not in a numeric format. You can try any of these two options. I already tested them and work perfectly:

Option 1

x=dec2bin(1024);
for i=1:11
  if strcmp(x(i), '0')
    i
  end
end

Option 2

x=dec2bin(1024);
for i=1:11
    if str2double(x(i)) == 0
        i
    end
end

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Answer 2

David Young 2011-8-20

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It's because the result from dec2bin is a character string. So each element of the array x represents a character, '0' or '1', from the binary representation of 1024. If you replace

if x(i) == 0

with

if x(i) == '0'

you will find you get the behaviour you expect (that is, it prints i=2, i=3 etc.)

The character '0' is usually represented by the numerical value 48, which of course is not equal to zero, so nothing is printed in your original code.