Weird problem in while loop: What is wrong with the input "48" compared to "47" and "49"????

Hi everyone!

I have a weird problem in a while loop with user input:

Within the while loop, the user is asked for the input of a number to be assigned to the variable insnr:

    1113  insnr = '0';
    1114  while insnr == '0';
    1115      insnr = input('Inselnummer [1 ... 999]  ?  ');   
    1116      answer = isempty (insnr);
    1117      while answer == 1;
    1118         disp('Gebe eine gültige Inselnummer ein [1 ... 999]  !!!'); 
    1119         insnr='0';
    1120         answer = isempty (insnr);
    1121      end
    1122  end

The code works fine for any number but the number "48".

Execution when using e.g. with the input "47" is as follows:

line 1113 [insr =’0’ char] --> 1114 --> 1115 insnr=47 [insnr=47 double] --> 1116 [answer=0] --> 1122 --> proceed with code properly at line 1123

A check on the input variable insnr yields:

K>> whos(insnr)

Name Size Bytes Class Attributes

insnr 1x1 8 double

Execution when using "48" is magically as follows:

line 1113 [insr =’0’ char] --> 1114 --> 1115 insnr=47 [insnr=47 double] --> 1116 [answer=0] --> 1122 --> 1115 and keeps on returning to this line until I use a number different from 48, e.g. 49

if I check on the input variable insnr:

K>> whos(insnr)

Name Size Bytes Class Attributes

insnr 1x1 8 double

Hence, it looks o.k.

Any idea what could be the problem here with the number "48" ... maybe a Hitchhiker's Guide to the Galaxy issue???

Thanks in advance.

Best, Magie

Answer 1

[Matt J]

It's because 48 is the ASCII code for '0'.

double('0')

ans = 48

char(48)

ans = '0'

48=='0'

ans = logical
   1

[Matt J]

Perhaps you meant to have,

insnr = 0;
while insnr == 0;
...
end

[magie]

Wow! Thanks a lot. That's the solution.

I already thought that it might be related to the translation into hex code or something. But wouldn't have thought that a simple input of a number could get into conflict of the Ascii translation of a string.

Thanks once more for this prompt reply.

Magie

[magie]

I meant to have the string, to leave the "0" as a number input possible. But I don't need and actually never used it. hence I can change line 1113 to insnr=0.

[Matt J]

Wow! Thanks a lot. That's the solution.

You're quite welcome, but please Accept-click the answer to indicate so.

[magie]

Accept-click done. Took some time to find the button.