Adding one value at the end of c++ array

Question

I want to add one more value into C++ array, and I have this piece of code:

void print_array(int *array, int size)
{
    for (int i = 0; i < size; ++i)
    {
        std::cout << array[i] << ' ';
    }
    std::cout << '\n';
}

void add_to_array(int *array, int size, int value)
{
    int *newArr = new int[size + 1];
    memcpy(newArr, array, size * sizeof(int));
    delete[] array;
    array = newArr;
    array[size + 1] = value;
}

int main(int argc, char const *argv[])
{
    int *array = new int[10];
    array[0] = 0;
    array[1] = 1;
    array[2] = 2;
    array[3] = 3;
    array[4] = 4;
    array[5] = 5;
    array[6] = 6;
    array[7] = 7;
    array[8] = 8;
    array[9] = 9;
    print_array(array, 10);
    add_to_array(array, 10, 11);
    print_array(array, 11);
}

I dont get any errors when I run it but the output is very wierd:

0 1 2 3 4 5 6 7 8 9 
0 0 -307888112 32767 4 5 6 7 8 9 1041

Any ideas how can I do it properly?

I know about vectors on lists in stl but i cannot use them so dont suggest it

Rather use a std::vector<int> array(10); and push_back() to add elements at the end. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Oct 25, 2020 at 13:44

MikeCAT · Accepted Answer · 2020-10-25 13:48:00Z

5

Function arguments of C++ are copies of what are passed and changing them won't affect what are passed. You should use references to have functions change what are passed.

Also note that now the new array has size + 1 elements and the index of the last element is size, not size + 1.

Fixed code:

void add_to_array(int *&array, int size, int value) // add & to make "array" a reference
{
    int *newArr = new int[size + 1];
    memcpy(newArr, array, size * sizeof(int));
    delete[] array;
    array = newArr;
    array[size] = value;
}

edited Oct 25, 2020 at 13:48

answered Oct 25, 2020 at 13:42

MikeCAT

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2 Comments

F.Hand Over a year ago

It's better for sure but when im printing second time the value at 10th place is 0 and not the pessed value into the function. I can change it in main. How can repair this?

MikeCAT Over a year ago

@F.Hand Fix the index for new element.

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