Splitting an array into multiple arrays c++

Question

What is the best way to split an array(mainArr) that holds 50 random integers into 5 different arrays that all contain 10 of the integers in each?

For example arr1 holds mainArr's 0-9 values, arr2 holds 10-19....

I have searched around but everything is splitting the array into two different arrays. Any help would be appreciated. Thanks.

Can you do something like int *arr1 = mainArr, *arr2 = mainArr + 10, ... — Weak to Enuma Elish
– Weak to Enuma Elish, Commented Nov 12, 2015 at 22:30
2 is multiple. Can't you apply the solution for "1 array to 2 arrays" to "1 array to N arrays"? — Kevin
– Kevin, Commented Nov 12, 2015 at 22:31
Exploit the fact is in C/C++, arrays act like pointers. Simply create 5 pointers, which point to the 0th, 10th, 20th, 30th and 40th cells in the array — SomethingSomething
– SomethingSomething, Commented Nov 12, 2015 at 22:39
It's not like Java or Python, in which array is kind of object that is defined with length that you can always query. In C/C++, you as a programmer are responsible to always know your array size. Just treat your 50-sized array as 5 10-sized arrays — SomethingSomething
– SomethingSomething, Commented Nov 12, 2015 at 22:41
@SomethingSomething but the 0th array contains all elements of mainArr? — Jean-Claude Colette
– Jean-Claude Colette, Commented Nov 12, 2015 at 22:41

nnn · Accepted Answer · 2015-11-12 22:34:34Z

3

To be a little more generic:

int mainArr[50];
int *arr[5];

int i;
for(i = 0; i < 5; i++)
    arr[i] = &mainArr[i*10];

And then access for example mainArr[10] as arr[1][0].

answered Nov 12, 2015 at 22:34

nnn

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4 Comments

I would change &mainArr[i*10] to mainArr + (i * 10), but it's only my opinion..

@Jason What do you mean? mainArr has only 1 dimension. arr[i] accesses the ith array

This helped alot, I am new to c++ so you will have to forgive me

@Kevin Sorry, you're right. The second array is ragged, not two dimensional.

Jason · Accepted Answer · 2015-11-12 22:48:17Z

0

Just define a function that maps each index, 0..49, into another index 0..4. The obvious function is division by 10. Modulus by 5 also works though.

int a[50];
int b[5][10];

for (size_t i = 0; i < 50; i++)
  b[i/10][i%10] = a[i];

or

int a[50];
int b[5][10];

for (size_t i = 0; i < 50; i++)
  b[i%5][i/5] = a[i];

See @nnn's solution for an example that re-uses the same memory.

answered Nov 12, 2015 at 22:48

Jason

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