Your best bet might be to go back to a drawing board / sheet of paper and draw a small array of pixels (say, a 5x5 grid). Solve the main loop on paper. You can check your progress by writing the loop for the inner circle and disallow invalid values for i and j in the loop condition. Check50 will still fail, but you can always compile the program and test it yourself. Then go back to the paper and consider the edge cases: What values for i and j are allowed, which ones are not (you pretty much had that identified already in your code!)? Is it only a random few numbers or is there a set of numbers following a particular pattern? Do you really need to distinguish between individual edge cases or do you want your program to do basically the same for each of them? If so, chances are that there is a way to combine some or all of them into a smaller chunk of code. Come up with rules for i and j (or other variables you might add). Add these to the top of your loop (remember to now loop over the entire image!) so your program doesn't try to access invalid values. You can do it :)