Write a text file with dynamically name from solve the system 972 equations

Hi, I have big problem with 972 equations and 972 variables which have from like: x1, x2,...,x27 (x will be change).

I must creat a txt file with:

x1, value(x1)

x2, value(x2)

....................

x27, value(x27)

Now I just can write a simple code like that:

id = fopen('inputabaqus.txt','w');

fprintf(id,'%s %.4f',"x1,",double(S.x1));

I don't want to repeat it 972 times so can I use the loop with using 'eval':

(open file)

for i=1:27

fprintf(id,'x(i)',double(S.xi)); (sorry I have not figured out how to write this just ideal)

end

(close)

Thank for your help !!!