Converting multiple if-else logic to for loop

Currently I have multiple if-else loops in my code, such as:

if (a > 2 && a < 4)
{
  // do something
}
else if (a > 4 && a < 6)
{
  // do something
}
else if (a > 6 && a < 8)
{
  // do something
}

... and so on.

is there a way to re-arrange this into a simpler FOR loop? or any other loop which can make the code more optimized?