I keep getting "error invalid types 'int int ' for array subscript"

Question

This is my code, any help is appreciated.
#include <iostream>
using namespace std;
int i; int j; int k; int m; int n; int b;
void product(int array[], int x=1)
{
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
for(k=0;k<b;k++)
{
x=x*array[i][j][k];
}
}
}
cout<<"Product: "<<x<<endl;
}
void suma(int array[], int y=0)
{
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
for(k=0;k<b;k++)
{
y=y+array[i][j][k];
}
}
}
cout<<"Sum: "<<y<<endl;
}
void numberElements(int array[], int z=0)
{
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
for(k=0;k<b;k++)
{
z=z+1;
}
}
}
cout<<"Total number of elements: "<<z<<endl;
}
int main()
{
int i, j, k, m, n, b, temp;
int arr[m][n][b];
cout<<"Array dimensions:"<<endl;
cin>>m>>n>>b;
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
for(k=0;k<b;k++)
{
cout<<"Insert value on ["<<i<<"]["<<j<<"]["<<k<<"] ";
cin>>arr[i][j][k];
}
}
}
cout<<endl;
cout<<"Array:"<<endl;
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
for(k=0;k<b;k++)
{
cout<<arr[i][j][k];
}
cout<<endl;
}
cout<<endl;
}
product(arr);
sum(arr);
numberElements(arr);
return 0;
}

Answer 1

1. You are passing a three-dimensional array to the functions, which in turn only expect a one-dimensional array. Passing multi-dimensional arrays is more complex:
https://stackoverflow.com/questions/13326021/how-to-pass-a-3d-array-as-a-parameter-to-function-c-also-do-global-variables
2. You are trying to set up the array before retrieving its dimensions, while the variables are still not initialized.
3. Variable-lenght arrays are anyway not standard C++ and only supported through compiler extensions. If you don't know the dimensions at compile time, you technically would have to allocate the array by yourself.
4. Using std::vector from the Standard Template Library could simplify the program by a lot:
https://en.cppreference.com/w/cpp/container/vector