Your frame1Function(...) logic is faulty - if frame1 is 3, then you can reach the frame1++ line, setting frame1 to 4, which exceeds your array dimension, before dropping out of the function. Do a check of frame1 before the function exits.

Alternatively, since you're passing the value 8 (one less than the array size) in runForward(...), you should be passing 3 runBackward(...).

Sigh. Your function is wrong. You're thinking along the right lines, but it's not implemented correctly. I'll explain why by stepping through your frame1Function. Below I've put line numbers in function, and have a couple of scenarios to show you where the function falls over.

void frame1Function(int maxframes)
{
1  if(frame1 >= maxframes)
2    frame1 = 0;
3  float comparisonVariable = 100 / frameRate;
4  if(ticks >= comparisonVariable)
  {    
5    ticks = 0;
6    if(frame1 >= maxframes)
7      frame1 = 0;
8    else
9      frame1++;
  }
}

We'll set frame1 = 3 & call frame1Function(3):

The condition in line 1 frame1 >= maxframes is true so line 2 is executed
> frame1 is now 0

If line 4 evaluates to true, then lines 5-9 are executed
> Line 6 evaluates to false, so line 9 is executed
> frame++ sets frame to 1

Hey, guess what, you've skipped a frame. frame1 went from 3 to 1, and missed out 0.

Ok, let's try out frame1 = 3 & call frame1Function(4):

Line 1 evaluates to false, so line 2 is not executed
> frame1 is still 3

If line 4 evaluates to true, then lines 5-9 are executed
> Line 6 evaluates to false, so line 9 is executed
> frame++ sets frame to 4

Hey, guess what, you've gone past the array boundary. frame1 went from 3 to 4.

To correct this behaviour, use the modulus operator ('%'), as in the following code:

void frame1Function(int maxframes)
{
  if(ticks >= (100 / frameRate))
  {
    ticks = 0;
    frame1++;
  }

  frame1 = frame1 % maxframes;
}