What's wrong with my 'NetCDF'?

I need to change some '*.nc' files to '*.mat' files. I choose to change them to text files first (as the code showed below), but there seems something wrong with my 'ncread'. I've put the warning in this picture. I wonder know if my code have some problem? Can my code changes those '.nc' files to text files and then save the text files? AND If there have something wrong, please tell me what should I do to solve it? THANKS!!!!

clc;
clear;

datadir='D:\Sort out\Original\China_hourly_rainfall_FiT_data_output\hourly_FiT_2008_output\';
filelist=dir([datadir,'*.nc']);
k=length(filelist);
b=[];

for s=1:k
    filename=[datadir,filelist(s).name];
    data=ncread(filename,'value');
        [r, c] = size(data);
        f = fopen(filename, 'wt');
        for i = 1 : r
            for j = 1 : c
                fprintf(f, '%5d', data(i, j));
            end
            fprintf(f, '\n');
        end
        fclose(f);

end

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/314002-error-reading-nc4-file-unknown-file-format-nc_enotnc#answer_244728

[CHANG XV]

I am sorry showing my appareciate to your help such late. It seems that my nc files are cruped, and I'm trying to find out the reason.