Passing an array by reference as a function parameter in C++ - c++

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 (3x3) 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

Answer 2

std::vectors are the way to go in C++ as variable-length arrays (such as int integers[C];) are forbidden.
I recommend typedefing these to make your code easier to read:
#include <vector>
typedef std::vector<int> row_t;
typedef std::vector<row_t> table_t;
Then you can declare:
void scanV(int Row, int value, int M, table_t& tableValues)
I've made this void since it doesn't return anything.
Your variables in int main() then become:
row_t integers;
table_t tableValues;
Watch out for this line:
tableValues[Row][i+value] == 1;
You probably meant to assign, rather than to check equivalence!
And please try to pick some more meaningful variable names than B, M, C...