### A small array is too big??

Hi everybody,

I apologize if the question is really easy... but I cannot figure out why I get an error message by my operating system (not the compiler, the program works if the array is say [50][50])

double x[1000][1000];

for (int i=0; i<100; i++)
{
for (int j=0; i<100; j++)
{
x[i][j] = i+j;
}
}

It is really weird since other programs like Matlab handle big 1000x1000 matrices without difficulties...

I am writing some code where I should make use of some 2-dimensional arrays of that size (ie.[1000][1000]) but I cant make it work...(though it works perfectly if I use 50x50 arrays)

Where is the problem??

Thanx

giulio
Well your for loops are wrong since they only loop to 100 instead of 1000. What is the error that you are getting? What compiler? What OS? 1000*1000 = 1000000 which is 1 million. That is pretty big for a stack array but I don't know how big your stack is.
Yeah, that's probably an 8 MiB array. Way too large for just about any stack.
http://www.cplusplus.com/doc/tutorial/dynamic/
I am sorry the loops were meant t go up to 1000 but that s not quite the point since even the program

double x[1000][1000];

produces the same error....!!

The compiler is Dev-C++ and the error I get is not from the compiler but from Windows itself...
I get the usual message "an error as occurred with Untitled1.exe" and at the end I have the option to Notify the problem to Microsoft and I choose "Dont's send"...

let me ask a question then...how come Matlab can easily handle a 1000x1000 matrix whereas c++, which is much more powerful, cannot do such a thing?
Because it's allocating it in the heap. Read the link I posted.
All of the array things, a million doubles, are on the stack. The reason Matlab handles them is because of the way it is coded. The stack is way too much.
why are you using doubles? Try short int unless your numbers are larger than 65535 or outside the range of -32768 to 32767.

Would that cut the memory requirements down 75%?
ok i am starting to understand... thank you

i am using double bc in the code i am writing those are decimals... actually they are probabilities, ie reals bw 0 and 1... you think there is a better type i can use..?

btw... i think that if i use the vector class in the std lib i can handle much bigger vectors

in fact the command

double x[1000000] //one million

causes the program to fail...whereas the command

vector<double> x(1000000]) //one million

is ok...

am i right?
http://www.cplusplus.com/doc/tutorial/variables/

scroll down to "Fundamental data types"
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