[Valmont]

Spot the differences. Especially how you had two variables called "seat". The second one is now called: Seat (starts with a capital letter).

#include <iostream>
#include <cstring>

using std::endl;
using std::cout;
using std::cin;

//-- static const unsigned ROWS = 7;
static const unsigned COLS = 4;
//--------------------------------------------------------------------------- char seat[7][COLS];

int main()
{
  for(unsigned i = 0; i < ROWS; ++i)
  {
    for(unsigned j = 0; j < COLS; ++j)
    {
    seat[i][j]= j+'A';
    }
  }

  for(unsigned i = 0; i < ROWS; ++i)
  {
    cout<< (i+1);
    for(unsigned j = 0; j < COLS; ++j)
    {
     cout<< " " << seat[i][j];
    }
    cout<< endl;
  }

  //Let's take seat at position [3,2]. Since indexes start at 0 we need to //substract 1: position = [3-1][2-1]. char Aisle; //for rows char Seat; //for coulumns
  cout<< "Please enter your desired seat no. (eg, 3A): ";
  cin >> Aisle >> Seat;
  unsigned row = Aisle -'0' - 1; //to calculate the row unsigned col = Seat - 'A';    //to calculate the column
  seat[row][col] = 'x';

  cout<<endl<<"After taking a seat:"<<endl<<endl;

  for(unsigned i = 0; i < ROWS; ++i)
  {
    for(unsigned j = 0; j < COLS; ++j)
    {
      cout<<seat[i][j];
    }
    cout<<endl;
  }

  //Remove the comment slashes below if your console "flashes away": //std::cin.get(); return 0;
}