// Function to add two big integers
Integer40 *big40Add(Integer40 *p, Integer40 *q)
{
    // Variable declarations
    Integer40 *result;
    int i, int1, int2, sum, carry = 0;

    // If any NULL pointers are passed in, return NULL
    if (p == NULL || q == NULL)
        return NULL;

    // Create the array to hold a big integer by calling our create function
    result = createIntArray(MAX40);

    // Take care of the cases when create function returns NULL
    if(result == NULL)
        return NULL;

    // Add both integers and store it in the digits array
    for(i = 0; i < MAX40; i++)
    {
        // If i is less than 40, make int1/int2 equal to the ith digit of the array, else make it 0
        int1 = (i < MAX40) ? p->digits[i] : 0;
        int2 = (i < MAX40) ? q->digits[i] : 0;

        // Add both integer arrays, making sure we carry if the addition results in a double-digit number
        sum = int1 + int2 + carry;
        carry = sum / 10;

        // Store the added integers in the digits array, ignoring the last carry
        result->digits[i] = sum % 10;
    }

    return result;
}