c++ overflow, merge sorting, inversion calculator

Question

My code is to calculate the number of inversion in the array. The calculation is working fine. The problem is that normally the range of unsigned int is 4,294,967,295 but it only accept the range of 2,147,483,647, equivalently, it doesn't recognize unsigned data type, instead accept it as signed.

unsigned int _mergeSort(int arr[], int temp[], unsigned int left, unsigned int right);
unsigned int merge(int arr[], int temp[], unsigned int left, unsigned int mid, unsigned int right);

unsigned int mergeSort(int arr[], int array_size) {
    int *temp = (int *)malloc(sizeof(int)*array_size);
    return _mergeSort(arr, temp, 0, array_size - 1);
}

unsigned int _mergeSort(int arr[], int temp[], unsigned int left, unsigned int right) {
    unsigned int mid;
    unsigned int inv_count = 0;
    if (right > left)   {

        mid = (right + left) / 2;

        inv_count = _mergeSort(arr, temp, left, mid);

        inv_count += _mergeSort(arr, temp, mid + 1, right);

        inv_count += merge(arr, temp, left, mid + 1, right);
    }
    return inv_count;
}

unsigned int merge(int arr[], int temp[], unsigned int left, unsigned int mid, unsigned int right) {
    unsigned int i, j, k;
    unsigned int inv_count = 0;
    i = left;
    j = mid; 
    k = left; 
    while ((i <= mid - 1) && (j <= right)) {
        if (arr[i] <= arr[j]) {
            temp[k++] = arr[i++];
        } else {
            temp[k++] = arr[j++];
            inv_count = inv_count + (mid - i);
        }
    }
        while (i <= mid - 1)
            temp[k++] = arr[i++];
        while (j <= right)
            temp[k++] = arr[j++];
        for (i = left; i <= right; i++)
            arr[i] = temp[i];
    return inv_count;
}

int main(int argv, char** args) {
    const int size = 100000;
    int arr[size];
    unsigned int i = 0;
    int converted;

    string input;
    fstream dataFile("IntegerArray.txt", ios::in);
    if (dataFile) {
        getline(dataFile, input);
        while (dataFile) {
            converted = atoi(input.c_str());
            arr[i++] = converted;           
            getline(dataFile, input);
        }
        dataFile.close();
    } else {
        cout << "error" << endl;
    }

    printf("Number of inversions are %d \n", mergeSort(arr, i));
    getchar();
    return 0;
}

There is no error. the number is overflowed so it go back to negative number.. — user3869196, Oct 25 '14 at 05:30
names starting with underscore, like `_mergeSort`, are reserved in the global namespace. — Cheers and hth. - Alf, Oct 25 '14 at 05:33
some general guidelines: use signed integers to represent numbers, use standard library collections like `std::vector` instead of allocating raw arrays dynamically, do not use `malloc` for allocation in C++ code ever, do not add "wait here" at the end of a program (just let your IDE do any such waiting, or run from command interpreter) — Cheers and hth. - Alf, Oct 25 '14 at 05:36
There's still a signed int in the signature of your `mergeSort` function (`int array_size`) - is that what you're looking for? — Jonathan Potter, Oct 25 '14 at 06:52
nop, I changed everything to unsigned but it still derive the negative number. — user3869196, Oct 25 '14 at 07:18

score 0 · Accepted Answer · answered Oct 25 '14 at 07:59

0

In your call to printf() you use a format specifier of %d which means signed integer. The actual value passed is an unsigned integer and the correct format specifier for that is %u. Fix the printf() call and test again.

Here is a reference for printf() and its formatting options.

answered Oct 25 '14 at 07:59

Blastfurnace

18,411
56
55
70

I tried u,x,o but still the same output. but thanks for good info. – user3869196 Oct 25 '14 at 08:05

c++ overflow, merge sorting, inversion calculator

1 Answers1