Finding the first triangle number with over five hundred divisors
Code


total += 2 is a bug. In case sum is a perfect square, and c happens to be its root, total shall be incremented by 1.
Using floating point (sqrt) in a number theoretical problem is dubious at best.
You don't need overallAdd. sum += i; suffices.
Naming looks arbitrary. The sum is a triangular number, total is a sum of divisors, so call them appropriately. Single-letter identifiers, like c shall be avoided.
Add your operators some breathing space.
Inner loop computes the number of divisors. Better factor it into a separate function.

Algorithm is brute force, which is never good, especially for Project Euler problems. This problem was discussed here many times. See this shameless self-plug for example.