Question

How can I pass an array, declared in main method by reference as a parameter to a function? Also the compiler wants dimentions, but when i give them with variables, the compiler gives errors of invalid integer dimensions of the array, here’s the code:

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int scanV(int Row, int value, int M, int (&tableValues)[])
{
for (int i = 0; i <= M; ++i)
{
    if (tableValues[Row - 1][i] == 1)
    {
        if (i + value <= M)
        {
            tableValues[Row][i+value] == 1;
        }
        if (i - value >= 0)
        {
            tableValues[Row][i-value] = 1;
        }
    }
}
}

int main()
{
int C, B, M;
cin>>C;
int integers[C];

for (int i = 1; i < C; ++i)
{
    cin>>integers[i];
}
cin>>B;
cin>>M;
integers[0] = B;
int tableValues[C][M + 1];
tableValues[0][B] = 1;
for (int i = 1; i < C; ++i)
{
    scanV(i, integers[i], M, tableValues);
}

return 0;
}

Answer 1

One simple solution is to use vectors. Consider this simple example:

#include <iostream>
#include <vector>

void f (std::vector<std::vector<int> > &v)
{
    for (int i = 0; i < 3; ++i)
        for (int j = 0; j < 3; ++j)
            v[i][j] = i * 3 + j;
}

int main()
{
    std::vector<std::vector<int> > v (3, std::vector<int> (3, 0));
    f (v);

    for (int i = 0; i < 3; ++i)
        for (int j = 0; j < 3; ++j)
            std::cout << v[i][j] << ' ';
}

In main, a 2D vector of ints (3×3) is created. The constructor shows 3 elements, all initialized with a vector of ints, which are in turn created with 3 elements initialized to 0.

Then, the vector is passed by reference to the function f, which assigns increasing values. When the vector is printed in main, it shows:

0 1 2 3 4 5 6 7 8

As you can see, their use is very similar to normal arrays, but they are actually contained, and provide easy access to a new level of programming using the STL.

In C++11, their use becomes even more familiar. You can assign vectors as follows:

std::vector<int> v0 = {2, 5};
std::vector<std::vector<int> > v1 { {1,2,3} , {4,5,6} , {7,8,9} };

Note that for vectors of multiple dimensions it’s a good idea to encapsulate it in a matrix class of some sort with an underlying 1D vector type instead.

Edit:

Here’s an example of initializing a 1D and 2D vector to specified elements. As seen above, this is easy in C++11, but if you have an array already, it’s still pretty quick.

int a [5] = {1,2,3,4,5}; //normal
std::vector<int> v1 (a, a +5); //create using beginning and ending addresses of a

int b[3][3] = { {1,2,3} , {4,5,6} , {7,8,9} }; //normal
std::vector<std::vector<int> > v2; //empty vector

for (int i = 0; i < 3; ++i) //3 in first dimension
    v2.push_back (std::vector<int> (b [i], b [i] + 3)); //push a vector with the appropriate 3 elements of b onto the back of v2

For going through one element at a time, you can do this:

std::vector<std::vector<int> > v (3, std::vector<int> (3));

for (int i = 0; i < v.size(); ++i) //v.size() == 3
    for (int j = 0; j < v [i].size(); ++j)
        adjustElement (v [i][j]); //replace with what you need