How big is too big?

I wrote a program for school that does Huffman compression. I use fgets to get my encoded string for decoding. Right now the encoded file is stored as one continous string (no newline). So I have been having to use numbers like 100,000 in the fgets call just to decode average size files.

fgets(array pointer, 100,000, infile);

Is there a better way to do this?