Problem with arrays

[shivamdabas]

I am having problem in writing the code for the problem "To assign the elements of 1-D integer array into 2-D array of integers such as if the array is 1,2,3,4,5,6 The resultant 2-D array should be like :
1 0 0 0 0 0
1 2 0 0 0 0
1 2 3 0 0 0
1 2 3 4 0 0
1 2 3 4 5 0
1 2 3 4 5 6
"
I really don't know how to begin at least give me some clue.
Thanks guys.

[o3hC5Di1]

Hi there,

You will have to use nested for loops to traverse both arrays:

int single_arr[6] = {1,2,3,4,5,6};
int multi_arr[6][6];

for (int i=0; i<6; i++) //loop single array]
{
    //single_array[i] is the current element

    for (int j=0; j<6; j++)
    {
        //multi_arr[i][j] refers to current element
    }
}

I've already given away a little bit more than I'd like, so I hope that helps.

All the best,
NwN

[shivamdabas]

I am still stucked

[keskiverto]

In what way?

[o3hC5Di1]

As Keskiverto asked, could you please be more specific?
What code have you written? Which problems do you encounter?

All the best,
NwN

[shivamdabas]

As said by NwN

int single_arr[6] = {1,2,3,4,5,6};
int multi_arr[6][6];

for (int i=0; i<6; i++) //loop single array]
{
    //single_array[i] is the current element

    for (int j=0; j<6; j++)
    {
          if((i==1)&&(j==1))
          multi_arr[i][j]=single_arr[j];
          else if((i==2)&&(j==1||j==2));     //going on like this for all values
          multi_arr[i][j]=single_arr[j];     //and in the end for else
                                             //statement putting multi_arr[i][j]=0
                        
    }
}

But this would be inefficient and wouldn't work for the array of unknown size. So, a bit more hint would be helpful

[o3hC5Di1]

Hi there,

If it needs to work for arrays of variable sizes, you will need to do the following:

- Ask the user how large the single array needs to be
- Create a dynamic array of that size
- Fill that array

In code:

int single_array_size;
//ask size
std::cout << "Size of single array: ";
std::cin >> single_array_size;
//create array
int single_array = new int[single_array_size];
//fill array
for (int i=0; i<single_array_size; ++i)
    single_array[i] = i+1;

You could even replace those if statements with 2 more for loops, one to fill up to the position i, the other to write 0 to the remaining positions. But, I'll leave that for you to figure out.

For completeness, I should mention that filling containers in this way can be done easily using the C++11 iota algorithm: http://en.cppreference.com/w/cpp/algorithm/iota

All the best,
NwN

[keskiverto]

Zero-initialization of the matrix. Easy, and done before the loop. That simplifies the loop.

How many items you have to copy to the first row of the matrix? How about to the nth row?