2D array problem.

[liangchenen]

on the stage 2 last problem. I did something like this

int main()
{
int grid[1000][1000];
cout<<"hi";
return 0;
}

then, after I compiled the program, the program didn't output the "hi", i was wondering why, then I made the variables global, then it worked. can anybody explain why it works/ doesn't work in detail?

[wtd]

liangchenen wrote:

on the stage 2 last problem. I did something like this

int main()
{
int grid[1000][1000];
cout<<"hi";
return 0;
}

then, after I compiled the program, the program didn't output the "hi", i was wondering why, then I made the variables global, then it worked. can anybody explain why it works/ doesn't work in detail?

Well, keep in mind that we when you allocate space for a 1,000 x 1,000 array, you've allocated somewhere between 4 and 8 MB of memory. On the heap (regular memory), this wouldn't be too horrible.

It is, however, a lot of memory to allocate on the stack, which is where this allocation is taking place.

[Andy]

three is a limit on how big an array is.. i had this problem during the ccc this year, turns out the max size was like [512][512] or something like it

[liangchenen]

How could I solve this problem?
do I just make the variables global?
or do I just make dynamic arrays like
int *array = new int [100];
but how could I do this for 2D arrays?

[wtd]

c++:

int *arr = new int[100][100]; for (int i(0); i < 100; ++i) {    arr[i] = new int[100]; }

But if you're looking to create a matrix, I suggest creating a class which wraps an array.

c++:

template <typename _t, size_t _r, size_t _c> class matrix {    private:       _t *data;    public:       matrix() : data(new _t[_r * _c]) { }       ~matrix() { delete [] data; }       size_t rows() const { return _r; }       size_t cols() const { return _c; }       _t operator()(size_t r, size_t c) const { return data[r * c]; }       _t& operator()(size_t r, size_t c) { return data[r * c]; } };

[Viper]

in an array how would you start at a number other than 0 eg
turing>> var f:array 30..100 of int

what would tht b in C++?? (i know i asked this be but i couldent find it again)

[wtd]

Viper wrote:

in an array how would you start at a number other than 0 eg
turing>> var f:array 30..100 of int

what would tht b in C++?? (i know i asked this be but i couldent find it again)

You don't. Arrays in C and C++ and many other languages (the only exceptions I can think of off the top of m head are Ada and Eiffel) always start with an index of zero.

[Andy]

y not just subtract 30 everytime u access it? it's the samething