CS Class 15 Today  More practice with arrays  Introduction to Multi-dimensional arrays Announcements  Programming project #4 due 10/23 by midnight ( .cpp to  Exam 2 is Tuesday, 10/28 during class

Programming project #4 Make sure your file “ballot.txt” is in the correct folder If your.net project is called CS114, go to the folder CS114, then click on CS114 again to go to the next folder. If you a Debug folder, you are in the correct location (do not go to the Debug folder)

Practice with arrays Problem: Generate 1,000,000 random numbers between 0 and 100. Find and print the number(s) that occurred the most often Tasks:  Generate 1,000,000 random numbers  Add to the appropriate counters 101 different counters Use an array for this  Find the counter(s) with the largest value  Print out those counters

Our algorithm Tasks:  Keep track of the number of occurrences of each number different counters Use an array for this  Generate 1,000,000 random numbers Based on the number, increment appropriate counter  Find the maximum value of all counters  Print out the number(s) with the largest counter The array counters keeps track of how many times we’ve seen each item  counters[0] contains the number of occurrences of 0  counters[1] contains the number of occurrences of 1  counters[2] contains the number of occurrences of 2  …  counters[100] contains the number of occurrences of 100 All counters initialized to 0

More on our algorithm Implement via main routine and three functions  Function One: Generates 1,000,000 random numbers between 0 and 100 Based on the number generated, increment a counter  Function Two Figures out which element in the array of counters is the largest  Function Three Prints all numbers where their counter matches the max counter Write the functions! void GenNumbers (int [ ]); int Largest (int [ ]); void PrintNums (int [ ], int); int main ( ) { int counters[101]; for (int a=0; a<101; a++) counters[a] = 0; GenNumbers (counters); int max=Largest(counters); PrintNums (counters, max); return 0; }

The functions void GenNumbers(int count[101]) { int value, seed = time(0); srand(seed); for (int a=0; a< ; a++) { value = rand() % 101; count[value] = count[value] + 1; } int Largest(int counters[101]) { int max = counters[0]; for (int a=1; a<101; a++) if (counters[a] > max) max = counters[a]; return max; } void PrintNums(int data[101], int value) { cout << "The number(s) that occurred the most : "; for (int a=0; a<101; a++) if (data[a] == value) cout << a << " "; cout << endl; }

Multi-dimensional Arrays Declaring two dimensional arrays int arr[5][4];  First subscript is rows  Second is columns first item is arr[0][0] last item is arr[4][3] How do you reference the locations indicated?  Location A  Location B  Location C  Location D  Location E B E D CA

Multi-dimensional Arrays Consider tic-tac-toe  Mark each position with a character ‘X’, ‘O’, space  Need two dimensions Logical Image Actual Physical Layout

Three more rules for arrays Must put each subscript in its own set of brackets x = arr[3][2]; arr[3,2] = 25; // this is NOT legal syntax When passing to a function: must provide dimensions for each (except first) subscript int funct1 (int array1[ ][10], … ); int funct2 (int array2[ ], … ); Can initialize arrays as you declare them int a[10] = {1,2,3,4,5,6,7,8,9,10}; int b[10] = {1,2,3,4,5}; int c[3][4] = { {1,2,3,4}, {5,6,7,8}, {9,10,11,12} };

Class Exercise: tic-tac-toe Want to write a game of tic-tac-toe  Main routine  Function to update the game board  Function to check if there is a winner  Function to print the board out after each move Main routine  Declare variables  Initialize the board  Loop (switch users) Enter a move Update the board Print the board Check to see if winner  Print the winner

Code for tic-tac-toe (part one) #include using namespace std; void MakeMove(char game[][3], int, int, char); void PrintBoard (char game[][3]); int CheckWinner (char game[][3]); int main ( ) { char game[3][3]; for (int a=0; a<3; a++) // initialize board for (int b=0; b<3; b++) game[a][b] = ' '; int done = 0, count = 0, row, col; while ( done == 0 ) { if (count%2 == 0) { cout << "Enter move (r,c) for X : "; cin >> row >> col; MakeMove (game, row, col, 'X'); } else { cout << "Enter move (r,c) for O : "; cin >> row >> col; MakeMove (game, row, col, 'O'); } done = CheckWinner (game); PrintBoard (game); count++; } if (done == 1) cout << "Winner was X" << endl; else if (done == 2) cout << "Winner was O" << endl; else // done == 3 cout << “Tie – cat’s game” << endl; return 0; } Function Prototypes & main

Code for tic-tac-toe (part two) void MakeMove ( char game[ ][3], int r, int c, char ch) { if (game[r][c] == ' ') game[r][c] = ch; else cout << "Illegal move, turn is lost!" << endl; } int CheckWinner ( char game[ ][3]) { return 0, 1 (‘X’) or 2 (‘O’); } void PrintBoard ( char game[][3]) { cout << "\t “ << endl; for (int a=0; a<3; a++) { cout << "\t| "; for (int b=0; b<3; b++) cout << game[a][b] << " | "; cout << endl; cout << "\t “ << endl; }

Class Exercises Code for tic-tac-toe is out on our class web page  Look under Sample Programs for Oct. 21.  It is missing the code for CheckWinner( ). Add the code for CheckWinner.  Three ‘X’ in a row, return 1  Three ‘O’ in a row, return 2  No winner and not full, return 0  All full, return 3

Ugly Code for CheckWinner int CheckWinner (char game[ ][3]) { if (game[0][0] == 'O' && game[0][1] == 'O' && game[0][2] == 'O') return 2; if (game[1][0] == 'O' && game[1][1] == 'O' && game[1][2] == 'O') return 2; if (game[2][0] == 'O' && game[2][1] == 'O' && game[2][2] == 'O') return 2; if (game[0][0] == 'O' && game[1][0] == 'O' && game[2][0] == 'O') return 2; if (game[0][1] == 'O' && game[1][1] == 'O' && game[2][1] == 'O') return 2; if (game[0][2] == 'O' && game[1][2] == 'O' && game[2][2] == 'O') return 2; if (game[0][0] == 'O' && game[1][1] == 'O' && game[2][2] == 'O') return 2; if (game[0][2] == 'O' && game[1][1] == 'O' && game[2][0] == 'O') return 2; if (game[0][0] == 'X' && game[0][1] == 'X' && game[0][2] == 'X') return 1; if (game[1][0] == 'X' && game[1][1] == 'X' && game[1][2] == 'X') return 1; if (game[2][0] == 'X' && game[2][1] == 'X' && game[2][2] == 'X') return 1; if (game[0][0] == 'X' && game[1][0] == 'X' && game[2][0] == 'X') return 1; if (game[0][1] == 'X' && game[1][1] == 'X' && game[2][1] == 'X') return 1; if (game[0][2] == 'X' && game[1][2] == 'X' && game[2][2] == 'X') return 1; if (game[0][0] == 'X' && game[1][1] == 'X' && game[2][2] == 'X') return 1; if (game[0][2] == 'X' && game[1][1] == 'X' && game[2][0] == 'X') return 1; int count = 0; for (int a=0; a<3; a++) for (int b=0; b<3; b++) if (game[a][b] == 'X' || game[a][b] == 'O') count++; if (count == 9) return 3; return 0; }

Good Code for CheckWinner int CheckWinner (char game[ ][3]) { for (int a=0; a<3; a++) { if (game[a][0] == 'O' && game[a][1] == 'O' && game[a][2] == 'O') return 2; if (game[0][a] == 'O' && game[1][a] == 'O' && game[2][a] == 'O') return 2; if (game[a][0] == ‘X' && game[a][1] == ‘X' && game[a][2] == ‘X') return 1; if (game[0][a] == ‘X' && game[1][a] == ‘X' && game[2][a] == ‘X') return 1; } if (game[0][0] == 'O' && game[1][1] == 'O' && game[2][2] == 'O') return 2; if (game[0][2] == 'O' && game[1][1] == 'O' && game[2][0] == 'O') return 2; if (game[0][0] == 'X' && game[1][1] == 'X' && game[2][2] == 'X') return 1; if (game[0][2] == 'X' && game[1][1] == 'X' && game[2][0] == 'X') return 1; int count = 0; for (int a=0; a<3; a++) for (int b=0; b<3; b++) if (game[a][b] == 'X' || game[a][b] == 'O') count++; if (count == 9) return 3; return 0; }

Better Code for CheckWinner int CheckWinner (char game[ ][3]) { int count = 0; for (int rv=1,char c=‘X’; rv<3; rv++, c = ‘O’) { for (int a=0; a<3; a++) { if (game[a][0] == c && game[a][1] == c && game[a][2] == c) return rv; if (game[0][a] == c && game[1][a] == c && game[2][a] == c) return rv; for (int b=0; b<3; b++) if (game[a][b] == c) count++; } if (game[0][0] == c && game[1][1] == c && game[2][2] == c) return rv; if (game[0][2] == c && game[1][1] == c && game[2][0] == c) return rv; } if (count == 9) return 3; return 0; }

End of Class 15