The statement of the problem seems ill-formed to me. How are these variables being "measured"? I could see reading in from a file of measurements. I could see calculating two variables from something else then writing out to a file. But I'm confused by the question as stated.
General thoughts: typically the two variables would be vectors (one element per measurement). You can concatenate vectors together into a matrix using array concatenation: [a,b]. You can write matrix data out to a file using sprintf.
