Program crashes sometimes when dynamically allocating memory [closed] - c++

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I am learning about pointers and dynamically allocating memory. So my question I guess is more of a technical issue. Whenever it seems I use the 'new' keyword to allocate memory for whatever I am doing, my program will sometimes crash. Sometimes not.
#include <iostream>
#include <iomanip>
#include <cstdlib> //I added this header file to get the NULL, this is not originally from the book
using namespace std;
int main(){
double *salesArry = NULL;
double total = 0.0, average;
int numDays, count;
cout << "How many days of sales figured do you wish to process ";
cin >> numDays;
salesArry = new double[numDays];
cout << "Enter the sales figures below.\n";
for(count = 0; count < numDays; count++){
cout << "Day " << (count + 1) << ": ";
cin >> salesArry[count];
}
for(count = 0; count < numDays; count++){
total += salesArry[count];
}
average = total/numDays;
cout << fixed << showpoint << setprecision(2);
cout << "\n\nTotal Sales: $" << total << endl;
cout << "\n\nAverage Sales: $" << average << endl;
delete [] salesArry;
salesArry = NULL;
return 0;
}
Full disclaimer: I am a student, this is NOT homework. I posted a book example. I copied it word for word and still my program crashes. My only reason for posting code is someone will proably ask "Can we see the code". Now the project I was working on is doing the same thing (crashes) so I doubt that both the book and I are wrong so that is why I'm guessing its a technical issue. The IDE I am using is Dev C++ and its the default compiler.
This is from Tony Gaddis's book "Starting Out with C++" Chapter 9, page 524

Answer 1

new double(numDays);
Whoops! When you transcribed the book, you made a typographical error. (I can confirm that the 8th Edition, which you said you're using, does not make this mistake (figure 9-14, et al.).
To dynamically allocate an array, you must use square brackets, otherwise you're just initialising one dynamically-allocated double with the value numDays.
new double[numDays];

Answer 2

salesArry = new double(numDays);
That line doesn't create an array of numDays doubles, it allocates a single double and initializes it to numDays.
To create an array, you would use:
salesArry = new double[numDays];
In C++, however, it is preferable to use std::vector instead of dynamically allocating arrays by hand:
std::vector<double> salesArray (numDays);