There isn't one single formula for a cycloalkene. Instead, the formula depends on the number of carbons in the ring. Here's how to determine the general formula:

* General Formula for Cycloalkanes: C_nH_2n (where 'n' is the number of carbons)

* Cycloalkenes: Since a cycloalkene has one double bond, you subtract two hydrogen atoms from the cycloalkane formula.

Therefore, the general formula for a cycloalkene is C_nH_2n-2.

Examples:

* Cyclopropene: C₃H₄

* Cyclobutene: C₄H₆

* Cyclopentene: C₅H₈

* Cyclohexene: C₆H₁₀