how to append a data (of specific format) from a text file to a csv file

Hi

I am looking for your advices regarding apending a data (of specific format) from a text file to a csv file. I have been trying to resolve the issue, yet not succeed.

Input: (A.txt):

3,4,5

Output:(B.csv)

3,4,5

will be printed in a cell.

I have read the data from A.txt as a string. And I am trying to write the string to the csv file by this way

fprintf('%s',data)

where data is the string representation of the reading from A.txt

But I found that, 3,4 and 5 have not printed in a single cell. It has spread to 3 cells of a row which I do not want. Would you please suggest me a way to resolve the issue?

thanks,