Problem with declaring a dynamic array of pointers to strings - c++

Question

While performing a practice assignment online I came across a problem which I am not able to solve.
The user has to a number(number of sentences he will be entering) and then proceed to enter the sentences one by one, which are to be stored as strings(by the way, declaring a dynamic array of pointers is mandatory). However, since the number of sentences is not a priori deducible, I know that the size of the array of pointers actually is the number of sentences but I can't figure out how to declare a dynamic array of pointers to strings.
Using something I had already known beforehand, I figured out how to do the same but with arrays of characters, not arrays of strings. The line that declared a dynamic array of pointers to dynamic arrays of chars looked like this:
char **ptr=new char*[n] {};
So with my understanding, this creates a pointer ptr which points to a dynamic array of pointers, the elements of which each point to one array of characters. I want to do something similar now, where the result should be that ptr is a pointer to a dynamic array of pointers, the elements of which each point to a string.
Can anyone help out? I'd be thankful!

Answer 1

I think what you are looking for is something like
std::size_t num;
std::cout << "enter the number of sentences\n";
std::cin >> num;
std::string *sentences = new std::string[num];
for(std::size_t i=0; i!=num; ++i) {
std::cout << "enter the " << (i+1) << "th sentence\n";
std::cin >> sentences[i];
}
/*
... (do something with the sentences, accessing them as sentences[i])
*/
delete[] sentences; // free the memory
Note that this style of coding is highly discouraged. The problem is the need to manage the allocated memory: avoid memory leaks and dangling pointers (including exception safety). The correct approach is to use a container or smart pointer. For example:
std::size_t num;
std::cout << "enter the number of sentences\n";
std::cin >> num;
std::vector<std::string> sentences{num};
for(std::size_t i=0; i!=num; ++i) {
std::cout << "enter the " << (i+1) << "th sentence\n";
std::cin >> sentences[i];
}
/*
... (do something with the sentences, accessing them as sentences[i])
*/
or
std::size_t num;
std::cout << "enter the number of sentences\n";
std::cin >> num;
std::unique_ptr<std::string[]> sentences{new std::string[num]};
for(std::size_t i=0; i!=num; ++i) {
std::cout << "enter the " << (i+1) << "th sentence\n";
std::cin >> sentences[i];
}
/*
... (do something with the sentences, accessing them as sentences[i])
*/
when in both cases you don't have to worry about calling delete: the allocated memory will be automatically deleted (even if an exception occurs).

Answer 2

You can avoid pointers completely and use
std::vector<std::string> input;
A std::array needs to know the size at compile time, and you learn this at runtime. The vector works like an array but can have items push_backed at runtime.
You could declare pointer to some strings, using n once you know it:
std::string * pInputs = new std::string[n];
but it's easier to use the vector.
Each pInput will be a string, as with the std::vector version.