How to use new and delete operator in C

Question

I'm presently studying C++ and have completed the following task in which I must transform an array from uppercase to lowercase and vice versa:

int main()
{
    char str[100];
    cout << "Enter anything: ";
    cin.getline(str, 100);

    //upper to lower vice versa
    for (int i = 0; i < 100; i++) {
        if (str[i] == 0x20)
        {
            continue;
        }
        str[i] ^= 0x20;
    }
    cout << "output: " << str;

return 0;

}

However, they want me to use the new[] and delete[] operators instead of declaring the numbers in an array, which is what this portion char str[100]; does. I've attempted to use it, but the notion confuses me. Is there anything you might suggest? Any assistance will be much appreciated! Thank you so much in advance!

Answer 1

int main(){
    char *str;
    int sz = 0;

    std::cout << "enter number of characters: ";
    std::cin >> sz;

    str = new char[sz + 1];

    std::cout << "Enter anything: ";
    std::cin.ignore();
    std::cin.getline(str, sz + 1);

    //upper to lower vice versa
    for (int i = 0; i < sz; i++) {
        if (str[i] == 0x20)
        {
            continue;
        }
        str[i] ^= 0x20;
    }
    std::cout << "output: " << str;

    delete[] str;
    return 0;
}

You allocate memory on the heap with new, and you deallocate memory with delete[].

Because the getline appends the 0 character at the end, you must set the array size to sz + 1.