Sum of 100 digit numbers - c++

Question

I have two arrays each containing 100 digits.I need to add corresponding digits from units place meaning from the end of the array.If there is a carry it should be added in the next index.It should return another array containing the sum.
Here is my code and something seems to be wrong .Help me
void sumOf100DigitNumbers(int num1[100], int num2[100], int sum[101]) {
int i, j = 100, k;
for (i = 99; i >= 0; i--)
{
if (sum[j] == 1)
{
}
else
sum[j] = 0;
k = sum[j] + num1[i] + num2[i];
if (k >= 10)
{
sum[j] = k % 10;
sum[j - 1] = 1;
}
else
{
sum[j] = k;
}
j--;
}
}
Method to test it
[TestMethod, Timeout(1000)]
void Test_sumOf100DigitNumbers2()
{
int a[100] = {6, 8, 3, 7, 8, 1, 2, 4, 6, 7, 2, 0, 6, 6, 7, 0, 0, 9, 4, 8, 2, 9, 6, 3, 1, 7, 2, 3, 0, 4, 4, 5, 0, 9, 7, 0, 8, 9, 2, 6, 9, 2, 8, 8, 0, 2, 8, 2, 6, 5, 3, 0, 5, 2, 2, 5, 8, 8, 6, 6, 2, 3, 6, 0, 7, 0, 9, 9, 0, 4, 6, 4, 0, 4, 5, 1, 9, 5, 1, 5, 3, 6, 6, 3, 2, 4, 0, 7, 7, 8, 4, 6, 8, 7, 8, 9, 1, 6, 9, 2};
int b[100] = { 4, 1, 4, 1, 5, 0, 1, 8, 4, 5, 9, 7, 6, 2, 2, 0, 1, 7, 2, 5, 0, 3, 6, 9, 0, 8, 7, 3, 0, 2, 7, 8, 6, 5, 7, 3, 6, 8, 4, 2, 9, 2, 4, 8, 2, 1, 1, 0, 6, 6, 2, 7, 2, 8, 9, 7, 2, 4, 2, 2, 7, 6, 0, 7, 2, 3, 8, 4, 2, 5, 4, 7, 1, 8, 9, 9, 7, 0, 3, 2, 5, 1, 9, 7, 1, 0, 0, 0, 2, 1, 1, 5, 9, 0, 0, 1, 6, 6, 9, 7 };
int ans[101] = { 1, 0, 9, 7, 9, 3, 1, 4, 3, 1, 3, 1, 8, 2, 8, 9, 0, 2, 6, 7, 3, 3, 3, 3, 2, 2, 5, 9, 6, 0, 7, 2, 3, 7, 5, 4, 4, 5, 7, 6, 9, 8, 5, 3, 6, 2, 3, 9, 3, 3, 1, 5, 7, 8, 1, 2, 3, 1, 2, 8, 8, 9, 9, 6, 7, 9, 4, 8, 3, 3, 0, 1, 1, 2, 3, 5, 1, 6, 5, 4, 7, 8, 8, 6, 0, 3, 4, 0, 7, 9, 9, 6, 2, 7, 7, 9, 0, 8, 3, 8, 9 };
int c[101];
sumOf100DigitNumbers(a, b, c);
Assert::AreEqual(true, areEqualArrays(ans, c, 101), L"sumOf100DigitNumbers() failed", 1, 2);
};
but my output is as follows:
Output

Answer 1

You never initialize c. This means that its contents are indeterminate. You can't predict what values it will contain.
So when you do this:
if (sum[j] == 1)
If one of those indeterminate values happens to be 1 then you're performing a carry you don't intend on doing.
You can initialize it as follows:
int c[101] = { 0 };
Then you can remove this entirely:
if (sum[j] == 1)
{
}
else
sum[j] = 0;