Array initialization

[Marcos Modenesi]

Is there a way to initialize an array according to user input?

Array lenght?

#include<iostream>
using namespace std;

int main(){
int cells;

cout << "Array lenght?" << endl;
cin >> cells;

int T[cells]={};

}

I can´t compile this, so, is there another way or I HAVE to initialize an array with a constant value???

Thanks in advance!

[Darkmaster]

#include<iostream>

int main()
{
	int size;
	
	std::cin >> size;
	int *A = new int[size];

	for(int i=0; i<size; ++i)
	{
		A[i] = i;
	}

	for(int i=0; i<size; ++i)
	{
		std::cout << A[i] << std::endl;
	}
	delete[] A;
}

input:3
output:

0
1
2

[Marcos Modenesi]

@ Darkmaster: Nice trick...
Ok, so just by creating it in the heap I can add "places" to my pointer A and therefore act as if I had a variable size array?

Anyway, I tried that and I got:

expected primary-expression before ']' token|
||=== Build finished: 1 errors, 0 warnings ===|

Then I erased []

int *A = new int[];

As if reserving only one variable, and it worked...

[Darkmaster]

changed it, now it works the way you wanted

simply mixed up the order and forgot the delete at the end :D

but yeah that "trick" works as long as the memory isn't used by anything else

[D80DSL3A]

Does that really work? Line 6 doesn't look right, and you should wait until after the user has entered the size before creating the array. Also, the memory should be freed in the end.

#include<iostream>

int main()
{
	int size;	
	std::cin >> size;
        int *A = new int[size];

	for(int i=0; i<size; ++i)
	{
		A[i] = i;
	}

	for(int i=0; i<size; ++i)
	{
		std::cout << A[i] << std::endl;
	}

        delete [] A;
}

EDIT: I was responding to Darkmasters code as it appeared several minutes ago.

[Darkmaster]

works, just run it

[Marcos Modenesi]

Thank you!

[Marcos Modenesi]

And what do you think of doing this?

#include<iostream>
using namespace std;

int main(){
int size;
cout << "size?" << endl;
cin >> size;

typedef int array[size];

array myArray;
for (int i = 0; i < size; i++){
    myArray[i] = i + 1;
    }

cout << '|' ;
for ( int i = 0; i < size; i++){
    cout << ' ' << myArray[i] ;
    }
cout << '|' << endl;
}

[Darkmaster]

i think its poorly indented and you are using namespace std

[maeriden]

I don't think that would compile

[Darkmaster]

wont compile since the arrray isn't a pointer

@ fun2code: look at the post above yours. that's excactly what i changed

[Marcos Modenesi]

@Darkmaster: how should I indent it? What´s wrong with namsepace std? I mean, if you really want to teach a noob!

@maeriden: it does compile, why do you think it would not?

[Darkmaster]

you write

int main(){
int size;
...
}

i would write

int main()
{
      int size;
      ...
}

that way you see the begging and end of a function. this gets helpful if you have loops inside loops and if statements inside and ...
to give you an example:

int main()
{
	for(int i=0; i<10; ++i)
	{
		for(int j=0; j<10;++j)
		{
			if(j==i)
			{
				...
			}
		}
	}
}

is just soooo much easier to read than

int main()
{
for(int i=0; i<10; ++i)
{
for(int j=0; j<10;++j)
{
if(j==i)
{
...
}
}
}
}

and it doesn't compile, since your arrays size is not constant

[Marcos Modenesi]

@ Darkmaster: I see, thanks, I´ll use your advice.

So now I´ve come to this point where the user can create bidimensional arrays according to his/her needs, thanks to typedef. Do you see any problems that could come up with memory usage?

#include<iostream>
using namespace std;

int main(){
   int m, n;
   cout << "m? n?" << endl;
   cin >> m >> n;

   typedef int matrix[m][n];

   matrix myMatrix;

   for (int i = 0; i < m; i++)
   {
       for (int j = 0; j < n; j++)
      {
            myMatrix[i][j] = 0;
      }
   }

   for (int i = 0; i < m; i++)
   {
       cout << '|';
       for (int j = 0; j < n; j++)
       {
           if (myMatrix [i][j]< 10) cout << ' ';
           cout << myMatrix[i][j] << ' ';
       }
       cout << '|' << endl;
   }
}

m? n?

2 3

| 0  0  0|
| 0  0  0|