If  $\oint \overrightarrow{\mathrm{E}.}\overrightarrow{\mathrm{dS}}=0 \mathrm{over} \mathrm{a} \mathrm{surface}$, then:

the electric field inside the surface is necessarily uniform.

the number of flux lines entering the surface must be equal to the number of flux lines leaving it.

the magnitude of electric field on the surface is constant.

all the charges must necessarily be inside the surface.