I know that int* array = new int [n]; allocates memory space in heap.
But if I declare something like that: int array[n]; in codeblocks it compile successfully, but if I move it to visual studio, it comes out of error.
What I want to ask is:
What does int[n] really do and how does it compare to heap allocation? What is the difference between them?
What the error may come out if I use int array[n] instead of int* array = new int [n];?
int array[n] declares an array on the stack, not the heap. In standard C++ n must be a compile time constant, however some compilers have an extension that allows for variable length arrays declared in this form without a compile time constant n. It's not standard and probably shouldn't be used.
int array[n] can cause a couple problems over int* array = new int [n];:
n is big enough you can cause a stack overflow. Or if the array is a class member and you create a large array of the class.array is a class member moving could be as expensive as copyingarray is a class member and you have given out pointers to the array and move the class, the pointers now refer to a post-moved object, or if random memory if the object was also destroyed. Either way, bad.
int array[n]?
GCC has an extension in C++ that allows int array[n] where n is not a compile time constant value. The standard language doesn't allow you to use non-constant value for n in such a case (it is allowed in C99).
If I understand your questions correctly, then I can answer both.
int array[10] is allocated on the stack, whereas int *array = new int[10] is allocated on the heap. Usually, stack arrays only work with a constant number of elements, so int array[n] is not allowed in C90 (as long as n is not constant).
MinGW (which is the version of the GCC compiler that codeblocks uses on windows) has an extension which does allow you to write int array[n] in C90 mode, where n is not constant. Visual C++ does not allow this.
when you write int array[n], that means you are performing a static allocation. i.e. memory will be allocated at the compile time. So using a variable length here will result in a compile time error.
Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C90 mode and in C++.