Why should I not use a standard loop to access a dynamic array?

Question

I have just started learning C++. I was looking at one example of the Accessing an array and the example was as the following:

a[i][j];
*(&a[0] [0]+2*i+j); /* Base address */
*(*(a+i)+j);

I am a bit confused about this example. Why can't I just create a standard loop like the following:

for(int row=0; row<i; row++ ){
    for(int col=0; col<j; col++ ){
       // Do something
    }
}

Answer 1

Your example lists 3 different methods to access an object at (presumably) the same index in a multi-dimensional array. This is something you would do inside a loop. So either do:

for(int row=0; row<i; row++ ){
  for(int col=0; col<j; col++ ){
     auto field = a[col][row];
  }
}

OR

for(int row=0; row<i; row++ ){
  for(int col=0; col<j; col++ ){
     auto field = *(*(a+col)+row);
  }
}

OR

for(int row=0; row<i; row++ ){
  for(int col=0; col<j; col++ ){
     auto field = *(&a[0] [0]+2*col+row);
  }
}