C++ arrays , and the "new" keyword

Question

So I have this code in here I've try to create a 2-D array with different sizes, first I declare 3 pointers then I assign different arrays to them and hope it works and it did well, but there is the problem , in the second code the compiler gives an error ( a value of type int* cannot be assigned to an entity type int ) so it means they are no longer pointers I think , but why is that , what am I missing here ? what is the biggest difference in these two codes other than one of them is declared in stack and other is on the heap

int main()
{
   int* arr[3];
   arr[0] = new int[5];
   arr[1] = new int[2];
   arr[2] = new int[6];

  delete[] arr[0];
  delete[] arr[1];
  delete[] arr[2];
}

//2nd Code

int main()
{
   int* arr = new int[3];
   arr[0] = new int[5];
   arr[1] = new int[2];
   arr[2] = new int[6];

}

and sorry for my baddd English

Don't do what you are doing now, and don't use nested vectors either, implement a proper 2d array instead. Read [this answer](https://stackoverflow.com/a/30464186/3002139) for example. — Baum mit Augen, Aug 05 '17 at 12:59
@BaummitAugen: OP doesn't want a matrix from his snippet. so `vector>` seems the more appropriate here. — Jarod42, Aug 05 '17 at 13:06
@Jarod42 Oh right. Poor reading on my part. Sorry to you and Ron. — Baum mit Augen, Aug 05 '17 at 13:08
@BaummitAugen Don't mention it. My now deleted comment was to use the vector of vectors. — Ron, Aug 05 '17 at 13:09
Baum has a point there. If you are using the matrix then use his proposed solution. — Ron, Aug 05 '17 at 14:44
Everyones' suggestions would be valid if this didn't sound like an assignment question to me. — Tanveer Badar, Aug 05 '17 at 15:10

score 1 · Answer 1 · answered Aug 05 '17 at 13:06

In the first program there is declared an array of pointers

int* arr[3];

In the second program there is allocated an array of integers

int* arr = new int[3];

So for example the expression

arr[0]

has type int.

If you want to allocate an array of pointers you should write

int ** arr = new int *[3];
    ^^               ^

In this case the expression

arr[0]

has type int * and you may write

arr[0] = new int[5];

C++ arrays , and the "new" keyword

1 Answers1