May I ask why you carry a gun, every day?
For the same reason that thousands of law-abiding Americans here
with valid handgun permits carry them: personal protection and
safety. And yes, I have had occasion to draw (but thankfully not
discharge) my handgun in public to protect myself in the past; that
incident is recounted in this thread (fifth post down).
The CZ100 is small and light enough to be easily concealed and
unobtrusive in everyday carry. Here's an image of it:

Can you please tell me:
a) What's the effective range of these types of weapons?
b) What's the length of their respective ammo.
That's a loaded question! I would say the effective range would
be those distances at which you can consistently hit your intended target
with reasonable accuracy. Scope-equipped large-caliber (44 Mag and
up) revolvers have been used by hunters here to take down some
pretty sizable game animals like deer and elk from distances
exceeding 100 yards.
My two Rugers pictured above have been used primarily to punch
nice, round holes in paper at around 25 yards. At this distance,
with open sights and shooting my target handloads from offhand, I'm
usually able to keep the groups consistently under 3". Our club has
an 18" cast iron gong mounted at the 200 yard backstop of the rifle
range. With my benchrested
Super Blackhawk, I am occasionally able to hit the gong, but one
has to aim high to compensate for bullet drop at that
distance.
As for the cartridge lengths, SAAMI specs for the 357 Mag. and 44
Mag. are 1.590" and 1.610" respectively. In other words, pistols in
those calibers have to be able to chamber cartridges up to those dimensions. There will
always be variations in overall cartridge length due to differences
in projectile weight and length.
For a visual perspective, here's an image of all the cartridges I
currently handload:

The 44 Mag. and 357 Mag. cartridges are fifth and sixth from the
left, respectively.
MG