Dear Muhammad Ramzan ,

I am a bit confused about that question;

for the cubic system we have the same lattice constant 'a' in all three orthogonal directions; we thus have the value of the lattice constant b = a and the value of the lattice constant c = a. That is why your software only provides a value of 'a', but nothing else.

For the c/a value you thus have c/a = a/a = 1.

But, may be, I have put your question in a wrong drawer of my brain...

Best regards

G.M.