how to modify data values for multiple text files

I want to modify the values for multiple text files at the same time how do i do that.

pathname = 'C:\Users\Documents\Shank\Onedrive\MATLAB\2017\2017-07'; % in the folder  specified. 
files = dir(fullfile(pathname, '*.txt' , ' ReadFcn' ,  @importdata)); % Get full path names for each text file
numFiles = fullfile({files.folder}, {files.name}); % Get a list of all txt files in the current folder, or subfolders of it.

for k=1:31 %there are 31 .txt files inside 2017-07
    filename=sprintf('[208] 2017-07-01%d.txt',k);
    T{1:1440,2:38}(T{1:1440,2:38}==0) = NaN; %change athh the zeroes and negative values to NaN
    T{1:1440,2:38}(T{1:1440,2:38} < 0) = NaN;
end

there are 31 files and in each file the zeroes and negativs numbers should be changed to NaN. I tried for 1 file how do fo this for 31 .txt files and save them .

Ps. there are 31 folders each folder with 31 files .

Answer 1

[KSSV]

txtFiles = dir("*.txt") ; 
N = length(txtFiles) ; 
for i = 1:N
    thisFile = txtFile(i).name ; 
    % do what you want 
end

[Vidhyashankar V]

i figured it out thanks !