I have a few straightforward questions:-

1. Is the following correct according to a normal c++ compiler?

   int arr[3][4];
   void func(int *a, int m, int n)
   {
    int i,j;
    cin>>i>>j; 
    cout<< a[i*n + j]; //is this way of addressing correct provided 0<=i<m and 0<=j<n
   } 
   
   int main()
   {
    func((int*)arr, 3,4);
   }
   

2. If the bounds of an array strictly has to be a constant expression, why doesn't the following generate compiler errors?

   int func(int m, int n)
   {
    int arr[m][n]; //m and n are not known until run time
   }