Bizarre Error

[pand9613]

Heres an interesting one:
I created a menu system to read in all the files in a directory and then list 
them 10 at a time allowing users to change pages or to select a file. As part 
of my error checking i use the input string option to make the user input as a 
string. To turn the users string input into a numerical input i used num2str. 
If the input is not numeric this returns an empty matrix which i can then act 
on, in this case returning to the top of the program. Now if i entered in 
say "hfdlas" (any erroneous string) in the user input i get the correct 
response. Also with "as576gf" (an erroneous alphanumeric string). However if i 
enter in "23dsjk" then i get parse errors when the code returns to the top. 
>From everything i can tell this should happen since from the top of the file 
nothing is affected by the user input.
I check the outputs of all lines and enterering "4sdjhg" is identical to 
entering "kjdhsf4" ie str2num on both produces an empty matrix and thus results 
in identical program flow and in no variables being redefined. So how is it 
that one produces an error while the other does not?
Cheers,
Peter Anderson


This is the error:

-------------------------------------------------------------
parse error:

>>> load -force materials/B45505.mtl
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 35
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 36
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 37
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 38
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 39
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 40
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 41
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 42
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 43
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 44
parse error:

>>> load -force materials/B45505.mtl
error: invalid character `' (ASCII 0) near line 49, column 45
parse error:

>>> load -force materials/B45505.mtl
error: evaluating for command near line 23, column 3
error: evaluating if command near line 11, column 2
error: evaluating while command near line 10, column 1
error: called from `getmatv2' in file `/composite/getmatv2.m'
error: called from `viewmat' in file `/composite/viewmat.m'
error: called from `opt' in file `/composite/opt.m' 
-------------------------------------------------------------

This is the code that produces the error:
-------------------------------------------------------------

function [Cmat]=getmat
global Ex
Cpage=1;

filelist=readdir('Materials');
mtlfiles=fnmatch('*.mtl',filelist);
mtlfiles=find(mtlfiles==1);
filelist=filelist(mtlfiles,:);

while Ex==0;
        if isempty(filelist)==1
                disp('No saved files')
                return
                else 
                Cpage_start= ((Cpage-1)*10+Cpage);
                if (Cpage*10)>length(mtlfiles)
                        Cpage_finish=length(mtlfiles);
                        else Cpage_finish=(Cpage*10);
                end
                
                disp('\n* Available Files *\n')
                matlist='';
                for i=Cpage_start:Cpage_finish
                loadline=['load -force materials/',filelist(i,:),' matname'];
                eval(loadline);
                matlist=[matlist;[num2str(i),'. ',matname]];
                end 
                disp(matlist)
                disp(sprintf('\n%.0f of %.0f Page(s)\n',Cpage,ceil(length
(mtlfiles)/10)))
                disp('Enter material number or (<>)to change page:\n\n  
        (b)ack\n                (e)xit\n')

                userin=input('>>','s');
                [h,w]=size(userin);
                if userin=='b'
                        return
                elseif userin=='e'
                        Ex=1;
                        return
                elseif userin=='>'  
                        Cpageok=Cpage+1;
                        if (Cpageok*10-10)>(length(mtlfiles)) | Cpageok<=0
                                disp('\nInvalid page number\n')
                                else Cpage=Cpageok;
                                continue
                        end                     
                elseif userin=='<'  
                        Cpageok=Cpage-1;
                        if (Cpageok*10-10)>(length(mtlfiles)) | Cpageok<=0
                                disp('\nInvalid page number\n')
                                else Cpage=Cpageok;
                                continue
                        end
                elseif userin==''
                continue
                
                else userin=str2num(userin)
                if userin==[]
                        disp('Invalid Input')
                        continue
                end

                if userin>length(mtlfiles)
                        disp('No such Material')
                        continue
                else
                        Cmat=[filelist(userin,:)];              
                return
                end
                end

        end
end


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