2D array as parameter in c++ - c++

Question

I would like to pass a 2D array to another function. I have an example of my code that I have all in the main function. However, the assignment requires that we split the code into a total of three functions, the main, adjmatrix, and adjlist functions.
All in the main function
#include<iostream>
#include<fstream>
using namespace std;
int main(void)
{
ifstream in;
char infile[40];
int c, u, v;
cout << "Please enter the input data file name(NO SPACES): ";
cin >> infile;
in.open(infile);
while(in.fail()) {
cout << "Please enter a CORRECT input data file name(NO SPACES): ";
cin >> infile;
in.open(infile);
}
//adj matrix
cout << "Adjacency Matrix" << endl;
in >> c;
int array[c][c];
for(int i=0; i<c; i++) {
for(int j=0; j<c; j++) {
array[i][j] = 0;
}
}
while(in >> u >> v) {
array[u][v] = 1;
}
cout << c << endl;
for(int i=0;i<c;i++) {
cout << i << " ";
for(int j=0;j<c;j++){
cout << array[i][j] << " ";
}
cout << endl;
}
cout << endl;
//adj list
cout << "Adjacency List" << endl;
cout << c << endl;
for(int i=0;i<c;i++) {
cout << i << " --> ";
for(int j=0;j<c;j++) {
if(array[i][j] == 1) {
cout << j << " ";
}
}
cout << endl;
}
in.close();
return 0;
}
This program outputs an adjacency matrix and adjacency list from the following input file
9
2 8
0 6
8 5
2 4
3 1
2 3
4 1
6 1
2 6
7 5
1 7
The following is the output
Adjacency Matrix
9
0 0 0 0 0 0 0 1 0 0
1 0 0 0 0 0 0 0 1 0
2 0 0 0 1 1 0 1 0 1
3 0 1 0 0 0 0 0 0 0
4 0 1 0 0 0 0 0 0 0
5 0 0 0 0 0 0 0 0 0
6 0 1 0 0 0 0 0 0 0
7 0 0 0 0 0 1 0 0 0
8 0 0 0 0 0 1 0 0 0
Adjacency List
9
0 --> 6
1 --> 7
2 --> 3 4 6 8
3 --> 1
4 --> 1
5 -->
6 --> 1
7 --> 5
8 --> 5
I read somewhere that passing a 2D array requires the second dimension to be entered. I also read something about it having to be a global constant? So I may have gotten a little crazy and went off on the crazy path on trying some things so please excuse some of the stupidity. The problem I think I am having is the actual array size comes from the file so I dont really understand where to go for declaring an array's second dimension with an actual value when int c is initialized to the first value in the input file. The following is my failed attempt at passing a 2D array. Enjoy:
#include<iostream>
#include<fstream>
using namespace std;
const int c;
void adjmatrix(istream &in, int array[][c]);
int main(void)
{
ifstream in;
char infile[40];
cout << "Please enter the input data file name(NO SPACES): ";
cin >> infile;
in.open(infile);
while(in.fail()) {
cout << "Please enter a CORRECT input data file name(NO SPACES): ";
cin >> infile;
in.open(infile);
}
in >> c;
int array[c][c];
adjmatrix(in, array);
in.close();
return 0;
}
void adjmatrix(istream &in, int array[][c])
{
int u,v;
for(int i=0; i<c; i++) {
for(int j=0; j<c; j++) {
array[i][j] = 0;
}
}
while(in >> u >> v) {
array[u][v] = 1;
}
cout << c << endl;
for(int i=0; i<c; i++) {
cout << i << " ";
for(int j=0; j<c; j++) {
cout << array[i][j] << " ";
}
cout << endl;
}
cout << endl;
}

Answer 1

You can allocate the array dynamically instead of statically defining it.
int i;
int **array;
in >> c;
array = new int*[c];
for(i=0;i<c;i++)
array[i] = new int[c];
adjmatrix(in, array,c);
The declaration of the function adjmatrix will be adjmatrix(istream &in, int **array,int c);

Answer 2

Following may help:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
void print_adjacency_matrix(const std::vector<std::vector<int>>& mat)
{
std::cout << "Adjacency Matrix" << std::endl;
std::cout << mat.size() << std::endl;
for(std::size_t i = 0; i != mat.size(); ++i) {
std::cout << i << " ";
for(auto e : mat[i]) {
std::cout << e << " ";
}
std::cout << std::endl;
}
std::cout << std::endl;
}
void print_adjacency_list(const std::vector<std::vector<int>>& mat)
{
std::cout << "Adjacency List" << std::endl;
std::cout << mat.size() << std::endl;
for (std::size_t i = 0; i != mat.size(); ++i) {
std::cout << i << " --> ";
for(auto e : mat[i]) {
if (e == 1) {
std::cout << e << " ";
}
}
std::cout << std::endl;
}
}
int main()
{
std::ifstream in;
std::string infile;
std::cout << "Please enter the input data file name(NO SPACES): ";
std::cin >> infile;
in.open(infile);
while(in.fail()) {
std::cout << "Please enter a CORRECT input data file name(NO SPACES): ";
std::cin >> infile;
in.open(infile);
}
int c;
in >> c;
std::vector<std::vector<int> > array(c, std::vector<int>(c));
int u, v;
while(in >> u >> v) {
array[u][v] = 1;
}
in.close();
print_adjacency_matrix(array);
print_adjacency_list(array);
return 0;
}