 <p>Your mistake is in translating 0 based to 1 based indexing. The arrays are 0 based. You're having them enter in a 1 based row. Then you want to add the 8 numbers around it. If they entered 0 based numbers and entered N, you'd want to sum [n-1], n, and n+1 for each row/column. To deal with 0 based, you want to do n-2, n-1, and n. But you're doing n-2 and n+2. You're also not calculating the middle of the rows anywhere near right.</p> <p>Best practice is not even to do the math like that. It would be to read in the row/column number, then immediately subtract 1 to make it 0 based, and deal with it as 0 based from then on.</p>