For example:
int size;
cout << "Enter array size" <<endl;
cin >> size;
int myarray[size];
I want the user to be able to enter the size of the array, but I keep getting an error message saying I'm not using a constant variable. When ever I search for an answer to this question, I get information about how to store a variable in an array (not what I'm looking for).
Variable length arrays are not part of the C++ standard, although they are part of the C99 standard and several compilers support them as an extension in C++ including gcc and clang, Visual Studio being one of the notable exceptions though.
The obvious C++ solution would be to use std::vector or possibly new although that means you have to worry about delete'ing the memory as well.
In C++ you can simply use std::vector, in your case a std::vector<int>.
You then need to include the <vector> header.
using std::vector;
int size;
cout << "Enter array size ";
cin >> size;
vector<int> myarray(size);
A std::vector takes care of managing memory for you, and it also has a handy push_back method to add an item at the end, expanding the array as necessary.
This means that you do not have to decide up-front on a specific size, but can simply add more items.
The proper way to handles this in C++03 and C++11 is to use a managed dynamic array type such as std::vector:
int size;
std::cout << "Enter array size" << std::endl;
std::cin >> size;
std::vector<int> myarray;
myarray.resize(size);
std::vector<int> behaves a lot like a raw array of ints. You can use [3] to access elements, as an example.
This is superior to managing the memory yourself, as ever experienced programmers lose track of memory.
There are proposals to add dynamically sized arrays to C++1y (the next iteration of C++) or later in an extension in a way that is somewhat compatible with C99 (an important difference is that sizeof(variable length array) in C99 is runtime evaluated, but not in C++). There are also proposals to add std::dynarray, which is a slightly less heavyweight std::vector style class with some possibility of automatic storage optimization. None of this is really needed to solve your problem.
std::vector is this post to do each step explicitly.
std::vector.std::vector<int>.std::vector<int, std::allocator<int>>.