I owned some years ago a p5 c and I just sold a Glock 26 to finance a new p5 c as I miss it so!
Both guns are 9 mm, with 8 + 1 shots for the Walther and 10 + 1 (or 12 + 1 with some finger extensions) for the Glock.
The Glock is smaller (160 x 110 x 28 mm versus 170 x 129 x 32) on paper. If you carry, you may find the Glock blockier as the Walther, whose slide and grips are "streamlined". Holsters for the Glock are plenty, and scarce for the Walther, although Sickinger, in Austria, has specific leather holsters for the p5 c which are of very high quality (www.sickinger.at).
On the range, due to different trigger modes, it is difficult to compare side by side both pistols. The Glock is very fast and easy to shoot accuratly, after you're accustomed to the Fast Action. The pointing is top notch. As a DA/SA, the p5 c may require more training for accurate double taps. The combinate slide/decocker lever is very smart. Felt recoil is comparable.
Reliability is questionable with the Glock (FTF), even with FMJs. I didn't experience any with the Walther, although I read about some malfunctions with HPs.
Being a little traditionnalist, I'm biased to the Walther. The quality is absolute top, the standart sights much better (you don't find/need aftermarket's!). The Walther p5 c is a must for the purist, you won't regret the bucks... If you do, you will sell it in a few seconds on this site.