Dynamic array crashed for more than 8 elements - c++

Question

#include<iostream>
using namespace std;
void arrayin(int x[], int n);
void arrayout(int x[], int n);
main()
{
int n, x[n];
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
cout << "Please enter the elements: " << endl;
arrayin(x,n);
cout << "Array is of " << n << " elements."<< endl;
cout << "Elements are as follow :" << endl;
arrayout(x,n);
}
void arrayin(int x[],int n)
{
for (int i = 0; i < n; i ++)
{
cin >> x[i];
}
}
void arrayout(int x[], int n)
{
for (int i = 0; i < n; i++)
{
cout << x[i] << "\t";
}
}
I'm new to programming.
It crashes for more than 8 elements, if n > 8 crashes.. but for n<8 works fine..
Dont know why!

Answer 1

Here is the problem:
int n, x[n]; // It is undefined behaviour
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
The correct way is (on your compiler with the variable-size-array extension):
int n;
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
int x[n];
The correct way using C++ is to use std::vector instead:
int n;
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
std::vector<int> x(n);
and you have to make some other changes to adapt std::vector.

Answer 2

The problem is here:
int n, x[n]; // <-- n is not yet initialized
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
cout << "Please enter the elements: " << endl;
arrayin(x,n);
You need this:
int n;
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
int x[n]; // << now n has been initialized
cout << "Please enter the elements: " << endl;
arrayin(x,n);
BTW: VLA (or dynamic arrays as you call them) are non standard in C++, but gcc (and possibily clang) has them as extension.

Answer 3

int n, x[n]; is the problem
You are declaring n that will have an indeterminate value. With this value you are declaring an array that will have an indeterminate size.
You are using C++, so use new keyword to create your array, after user input:
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
int *x = new int[n];
// your stuff
delete x;

Answer 4

Declare your array after taking input for n.
#include<iostream>
using namespace std;
void arrayin(int x[], int n);
void arrayout(int x[], int n);
main()
{
int n;
cout << "Please enter the number of elements in the array: " << endl;
cin >> n;
int x[n];
cout << "Please enter the elements: " << endl;
arrayin(x,n);
cout << "Array is of " << n << " elements."<< endl;
cout << "Elements are as follow :" << endl;
arrayout(x,n);
}
void arrayin(int x[],int n)
{
for (int i = 0; i < n; i ++)
{
cin >> x[i];
}
}
void arrayout(int x[], int n)
{
for (int i = 0; i < n; i++)
{
cout << x[i] << "\t";
}
}
This code works. The problem is when you declare array with no value for n the array will be initialized with whatever is on stack from past. Variable length arrays require the value. So declare the array later.
Someone downvoted without any reason.
Edit: Variable length arrays are not part of ISO C++. To write standard compliant C++ code you should use -pedantic flag with g++ or clang.
You have two simple choice. Either use std::array for fixed length arrays or std::vector for dynamic arrays.