Run time error with array

Question

I can't understand why I get the run time error:

the variable ia is being used without being initialized.

However, as far as I can see, I have initialized it.

#include <iostream>
using namespace std;
int main()
{
 //array dimensions
 const int row_size = 2;
 const int col_size = 4;
 //array definition
 int ia[row_size][col_size] = {{0, 1, 2, 3},{5, 6, 7, 8}};
 cout << ia[2][4];
 system("PAUSE");
 return 0;
}

• rid: ia[2][4] is invalid. Counting starts from 0, not 1. You probably meant ia[1][3].

Answer 1

C++ array indexes are zero-based. So to access the fourth column of the second row, you need to access ia[1][3].

• Daniel Gratz: Ah such a simple oversight... thanks will give you the green mark.

Answer 2

ia[2][4]

doesn't exist.

ia[0..1][0...3]

all exist, however.

Try:

cout << ia[1][3];

---

Arrays in C++ start with the index 0. 1 is actually the 2^nd element. So:

int a[2] = {42, 50};
std::cout << a[0] << a[1]; // prints 4250
std::cout << a[2]; // a[2] doesn't exist!

Answer 3

Array indexes start from 0, so your ia[2][4] will be out of bounds. Should be ia[1][3].

Answer 4

Arrays are 0-based, i.e. the first element in an array a is a[0]. So the last element in an array of 4 elements would be a[3]. In your case ia[1][3] would give you the sought element I believe.