  Accurate stellar parameters are needed in numerous domains of astrophysics.
The position of stars on the H-R diagram is an important indication of their
structure and evolution, and it helps improve stellar models. Furthermore, the
age and mass of stars hosting planets are required elements for studying
exoplanetary systems. We aim at determining accurate parameters of a set of 18
bright exoplanet host and potential host stars from interferometric
measurements, photometry, and stellar models. Using the VEGA/CHARA
interferometer, we measured the angular diameters of 18 stars, ten of which
host exoplanets. We combined them with their distances to estimate their radii.
We used photometry to derive their bolometric flux and, then, their effective
temperature and luminosity to place them on the H-R diagram. We then used the
PARSEC models to derive their best fit ages and masses, with error bars derived
from MC calculations. Our interferometric measurements lead to an average of
1.9% uncertainty on angular diameters and 3% on stellar radii. There is good
agreement between measured and indirect estimations of angular diameters (from
SED fitting or SB relations) for MS stars, but not as good for more evolved
stars. For each star, we provide a likelihood map in the mass-age plane;
typically, two distinct sets of solutions appear (an old and a young age). The
errors on the ages and masses that we provide account for the metallicity
uncertainties, which are often neglected by other works. From measurements of
its radius and density, we also provide the mass of 55 Cnc independently of
models. From the stellar masses, we provide new estimates of semi-major axes
and minimum masses of exoplanets with reliable uncertainties. We also derive
the radius, density, and mass of 55 Cnc e, a super-Earth that transits its
stellar host. Our exoplanetary parameters reflect the known population of
exoplanets.
