ASSIGNMENT: TEXT FILES Write a function called char_counter that counts the number of a certain character in a text file. The function takes two input arguments, fname, a char vector of the filename and character, the char it counts in the file.

When testing with '' your solution returned -1 which is incorrect. (0)

This error pops up while doing the assignment.

can anyone tell me why is this error popping and the meaning of the statement mentioned above.

when the character is ' " ' then i get a finite answer. and when the character is ' ' ' then too answer is a finite number. but i dont understand what the above bold text means....

my code

function charnum = char_counter(fname,character)
fid=fopen(fname);
if fid< 0
    charnum = -1;
    return;
end
if strcmp(character,'')==1
    charnum=0;
    return;
end
if double(character)>=35 && double(character)<=43 && double(character) ~=39 && double(character) ~= 41 && double(character) ~= 40 
    charnum = 0;
    return;
end
if double(character) >=60 && double(character) <=64 && double(character) ~= 63 
    charnum = 0;
    return;
end
if double(character) == 81 || double(character) == 88 || double(character) == 90
    charnum = 0;
    return;
end
cc = fgets(fid);
sumv=0;
while ischar(cc)
    z = sprintf('%s',cc);
    k = strfind(z,character);
    sumv = sumv + length(k);
    cc = fgets(fid);
end
charnum = sumv;
if charnum == 0
    charnum =-1;
    return;
end

[Walter Roberson]

Why are you special-casing Q, X, Z ? Why are you special-casing the special characters?

Special-casing '' might be reasonable, but it looks to me as if none of those special cases are needed.

What is wrong is that when no copies of the character are detected, then because the sum will be 0, charnum will be assigned 0, and then your if charnum == 0 will be triggered, causing you to return -1. -1 should only be returned if there is a problem with the input you were given, and if the character simply is not found then the result should be 0.

[Rakshith R]

thanks for clearing this

but when i remove those statement i get a error stating

char_counter('simple.txt',11) failed

why so

[Shubham Pandey]

The basic error this code is generating is that when you pass '' as character and if it reads 0 and stores it in charnum, this charnum is getting changed to -1 due to last if block. That is why, the error is showing up. Therefore, it is advisable to remove the last if block. Instead, you may add additional OR condition in the first if block to check for the validity of the character in addition to fid<0.

Answer 1

[Walter Roberson]

You are apparently using some kind of automated assignment assessing software. You submitted an assignment for grading. The course software tried passing '' (the empty character vector, equivalent to char([]) ) to your function, and your function returned the value -1 which is not what the assignment specifies should be returned for that input, so it told you that you are wrong.

We do not know what assignment you were doing, or what the correct answer was to that input. You will need to re-read the question more carefully to see what you should have responded with.

I speculate that you were doing the assignment that has been going around about counting the number of matches of a character in a file. The assignment other people have been posting requires that -1 be returned if the input is invalid. I suspect that you are seeing the '' (empty character vector) and considering it to be invalid and so returning -1, but that if you were to read the assignment more carefully you would find that the assignment considers '' to be a valid input and that the number of matches you would expect for it would be 0. Be careful with your validation tests: isempty() is true for both [] and '' .

Answer 2

[Jaimin Motavar]

can some tell me what is the my mistake in this code?problem is written in comment secssion.

function charnum = char_counter(filename,b)
charnum=0;
if ~ischar(b)
    charnum=-1;
    return;
end
fid = fopen(filename,'rt');
if fid<0
    charnum=-1;
    return;
end


    

oneline= fgets(fid);
while ischar(oneline)
    a=sprintf('%s \n',oneline);
    c=findstr(b,a);
    [m,n]=size(c);
    charnum=charnum+n;
    oneline=fgets(fid);
end

end

[Jaimin Motavar]

[Ajith Thomas]

can you tell me the function of fgets here?

[Walter Roberson]

fgets reads one line from the file including any delimiter

Answer 3

[Ajith Thomas]

my question is which all characters should be eliminated? on this question?

[Walter Roberson]

There are different versions of the assignment around. In the most common case, there are no characters that should be eliminated. The tests against Q V and so on were hacks to deal code mistakes the user had made.

A common mistake people make is that they are returning -1 when a valid input is not found. They should be returning 0 instead. -1 is reserved for file not found or invalid input argument.

[Walter Roberson]

Hint: you do not need to attempt the fopen() if a is not a char.

Answer 4

[Preethi Vannal]

I passed 3 assessments out of 4 for this same question.

My code:

function charnum = char_counter(fname,ch)
if isfile(fname)
    fid=fopen(fname,'rt')
    if (fid>0 && ischar(ch))
        ct=0;
        oneline=fgets(fid);
        while ischar(oneline)
            if(strfind(oneline,ch))
                ct=ct+count(oneline,ch);
            else
            charnum=-1;
            end
            oneline=fgets(fid);          
        end
        charnum=ct;
    else
        charnum=-1;
    end
else
    charnum=0;
end
fclose(fid);
end
     I am not able to get idea to pass this 4th assessment.
     Can anyone please help me?

[Walter Roberson]

If isfile() fails then you return charnum=0 but the assignment requires charnum -1 for that case.

            if(strfind(oneline,ch))
                ct=ct+count(oneline,ch);
            else
            charnum=-1;
            end

What is the reason you are setting charnum if you do not happen to find the desired character on one particular line?

[Stephen23]

@Preethi Vannal : you should replace the two if statements with one:

if fid<3 || ~ischar(ch)
    ...
else
    ...
end

[Mohymen Kushal]

Don't close the file. fopen will return -1 if the file dosen't exist. But if you close it with fclose it won't.

[Walter Roberson]

It is good practice to fclose() any file you fopen() unless you are returning the handle of the file (or recording it internally.)

However, the code posted attempts to fclose() the file even if the exist() test failed, which is a problem because if exist() failed then the variable fid would not have been assigned to.

Answer 5

[tshering lhamo]

hello, my function gives the error "test with all visible characters-failed". please help me understand where I made a mistake. thank you!

function charnum=char_counter(fname,character)
fid=fopen(fname,'rt');
if ~ischar(character)||fid<0
    fprintf('error opening file\n');
    charnum=-1;
    return;
else
    fname=fgets(fid);
    charnum=0;
    for ii=1:length(fname)
        char_n=count(fname(ii),character);
        charnum=charnum+char_n;
    end 
end
fclose(fid);

[Rik]

You don't close the file if the character input is invalid, and you only read a single line. Also, as you're going character by character you don't really need the count function. And why do you store the file contents in fname? That name doesn't describe the contents at all.