Q:
How to create a dynamic array
I'm writing a small program that requires to use a dynamic array. I am not sure what I'm doing wrong, and I have been banging my head against the wall with this.
Here's my C file:
#include
#include
using namespace std;
int main() {
const int maxElements = 4;
int numberOfItems = 0;
string numArr[maxElements];
cout << "Enter an integer to create the array: ";
cin >> numberOfItems;
for (int i = 0; i < numberOfItems; i++) {
cout << "Enter another integer to create the array: ";
cin >> numArr[i];
}
cout << endl << "You entered: ";
for (int i = 0; i < numberOfItems; i++) {
cout << numArr[i] << " ";
}
cout << endl << endl;
}
So, in the "Enter an integer to create the array:" section, I want to create an array that goes from 0 to 4. In the "Enter another integer to create the array:" section, I enter an integer, which is stored as my array's first element. Then I want to create a second entry. I don't want the array to grow itself every time, I just want it to start over at 0 every time.
I thought about using string::append, but then I realized, I'm not using c++.
I have a feeling I'm using new incorrectly, I have very little experience with pointers.
What am I doing wrong?
A:
First of all the code you've shown us is not a real dynamic array because it only creates a sequence of arrays which get destroyed when the application finishes.
Second, unless your intent is only to compile and run it on windows (which has very small dynamic arrays) you are going to have to learn a bit of C++. The C++ way of doing this is shown below. As it happens, I think you have got the syntax wrong.
#include
#include
using namespace std;
int main() {
const int maxElements = 4;
int numberOfItems = 0;
string* numArr= new string[maxElements];
cout << "Enter an integer to create the array: ";
cin >> numberOfItems;
for (int i = 0; i < numberOfItems; i++) {
cout << "Enter another integer to create the array: ";
cin >> numArr[i];
}
cout << endl << "You entered: ";
for (int i = 0; i < numberOfItems; i++) {
cout << numArr[i] << " ";
}
cout << endl << endl;
delete[] numArr;
return 0;
}
However, in C++ it is usually preferred to use a container class instead of an array.
A:
You've used the wrong data type to store the elements. You can't use an int for this, unless you want to re-implement a linked list in C. If you want an array you need to use the built-in std::string.
A few other comments:
Strings are not null terminated, you need to specify that the strings will be zero terminated
You should use std::vector instead of an array.
Prefer a "using namespace std" to your "using std::cout", there's no reason to use fully qualified names
This should work for you:
#include
#include
using namespace std;
void foo(int n) {
string arr[4];
cout << "Enter a number of elements for the list: ";
cin >> n;
for (int i = 0; i < n; i++) {
cout << "Enter another number to create the array: ";
cin >> arr[i];
}
cout << "\n You entered: " << endl;
for (int i = 0; i < n; i++) {
cout << arr[i] << " ";
}
cout << "\n\n" << endl;
}
int main() {
if ( cin.get() != '\n') foo(0);
cout << endl;
return 0;
}
A:
You don't need to create your own array, C++ already has the built in string for that.
Also your for loop is wrong, it should be numElements, not i, i is an iteration variable, numElements is a number.
std::string numArr[maxElements];
This line is wrong:
cin >> numArr[i];
You can just do this:
cin >> numArr;
And finally:
std::cin.getline(tempNum, 1000); // Reads numbers until the enter key is hit.
Change that line to:
cin >> tempNum;
And add one more thing, instead of int maxElements use std::string::size(), because you are not using the string array in any other ways than iterating on it with an index, so std::string::size() is a better option than hardcoding maxElements with 4.
