I have been having difficulty solving the N Queen problem, I am able to implement most of my functions, but the function that places the Queen recursively with backtracking. The placeQueens function is using a provided pseudocode that is required for the project. I had to create the array on the heap that is pointing to boardPtr, which is also required. I have a while loop condition that I have but I am not sure if it's correct. I have tried looking online for similar code but none of them were able to help me.
Here is my code:
#include <iostream>
#include "ChessBoard.h"
int main()
{
// Create a board
ChessBoard myBoard;
/* Loop through board sizes from 3 to 13.
Since 3 and 13 are invalid you should see
board sizes 4 and 12 twice. */
for (int i = 3; i <= 13; i++)
{
myBoard.setSize(i);
/* Attempt to solve the N-Queens Problem. If the solve
code is working it should find solutions for all
sizes. */
if (!myBoard.solve())
std::cout << "Sorry, no solution was found for board size "
<< myBoard.getSize() << "." << std::endl << std::endl;
else
{
std::cout << "Size " << myBoard.getSize()
<< " solution:" << std::endl;
myBoard.displayBoard();
std::cout << std::endl << std::endl;
}
}
return 0;
}
#include "ChessBoard.h"
#include <iostream>
using namespace std;
bool ChessBoard::placeQueens( int column)
{
int row = 0;
if (column >= boardSize)
{
// The board is filled, problem is solved.
return true;
}
else
{
while (row < boardSize && column < boardSize) // unconsidered rows exist in column
{
if ((canPlace(boardPtr, row, column)) == true) //[row][column] is unattacked
{
//Place a queen in the un - attacked square.
boardPtr[row][column] = 'Q';
//Do a recursive call to try and place queens in subsequent columns :
if (!placeQueens(column + 1))
{
//If we’re here, placement of the last queen resulted in a dead end; no solution could be found.Remove the last queen placed.
boardPtr[row][column] = '*';
//Move to next row so search can continue in next iteration.
row++;
}
else
{
// If we’re here, recursive calls were able to place queens in all columns to the right of column, the problem is solved.
return true;
}
}
else
{
//Square is attacked, move to next row.
row++;
}
}
//All rows have been considered in column without a successful queen placement.Backtrack by returning false.
return false;
}
}
bool ChessBoard::canPlace(char** boardPtr, int row, int column)
{
int i, j;
// Check row
for (i = 0; i < column; i++)
if (boardPtr[row][i] )
return false;
// Check upper diagonal
for (i = row, j = column; i >= 0 && j >= 0; i--, j--)
if (boardPtr[i][j])
return false;
// Check lower diagonal
for (i = row, j = column; j >= 0 && i < boardSize; i++, j--)
if (boardPtr[i][j] )
return false;
return true;
}
ChessBoard::ChessBoard()
{
boardSize = 8;
boardPtr = nullptr;
}
ChessBoard::ChessBoard(int size)
{
if (size < 4)
{
boardSize = 4;
}
else if (size > 12)
{
boardSize = 12;
}
}
ChessBoard::~ChessBoard()
{
}
int ChessBoard::setSize(int size)
{
delete[] boardPtr;
//Initialize array at size 4
if (size < 4)
{
boardSize = 4;
char** chessBoard = new char* [4];
for (int i = 0; i < 4; i++)
{
chessBoard[i] = new char[4];
}
// Point initialized ChessBoard to boardPtr
boardPtr = chessBoard;
// Fill ChessBoard with *
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
boardPtr[i][j] = '*';
}
}
}
//Initialize array at size 12
else if (size > 12)
{
boardSize = 12;
char** chessBoard = new char* [12];
for (int i = 0; i < size; i++)
{
chessBoard[i] = new char[12];
}
// Point initialized ChessBoard to boardPtr
boardPtr = chessBoard;
// Fill ChessBoard with *
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
boardPtr[i][j] = '*';
}
}
}
//Initialize array at given size
else
{
boardSize = size;
char** chessBoard = new char* [size];
for (int i = 0; i < size; i++)
{
chessBoard[i] = new char[size];
}
// Point initialized ChessBoard to boardPtr
boardPtr = chessBoard;
// Fill ChessBoard with *
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
boardPtr[i][j] = '*';
}
}
}
return 1;
}
int ChessBoard::getSize()
{
return boardSize;
}
bool ChessBoard::solve()
{
int column = 0;
if (placeQueens(column) == false)
{
return false;
}
else
{
return true;
}
}
void ChessBoard::displayBoard()
{
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
cout << boardPtr[i][j] << " ";
}
cout << endl;
}
}
#ifndef CHESSBOARD_H
#define CHESSBOARD_H
class ChessBoard
{
private:
char** boardPtr;
int boardSize;
bool placeQueens( int column);
bool canPlace(char** boardPtr, int row, int col);
public:
ChessBoard();
ChessBoard(int size);
~ChessBoard();
int setSize(int size);
int getSize();
bool solve();
void displayBoard();
};
#endif
Interesting task you have! I decided to implement my own code from scratch for solving N Queen problem. Actually I implemented it for any board size N, not just equal to 8.
I didn't fix bugs in your code, but instead implemented my own solution. Although it may be not the answer you want, still it would be a good thing from educational point of view. Hoping that there would be other answers later that are fixing bugs in your code, as you wished.
I made code very optimized, so it is not very simple from first side, but solves task very fast, using BackTracking, with several extra techniques of speeding it up.
After program finishes it prints to console all solutions in a nice form. Please scroll down below the code to see example of console output.
First program has some extra descriptive comments to show what's happenning in program.
Notice that I provided two codes below, first is simplified version, that is more easy to understand, so it is better from educational point of view. Second code is advanced one, it is more difficult, but solves task fast. Please look at first code if you want just to learn basics, and look at second code if you want to learn advanced techniques.
Simplified:
Try it online!
#include <iostream>
#include <vector>
#include <string>
void Output(std::vector<std::vector<bool>> & board, std::vector<std::string> & lines, bool last);
void Solve(std::vector<std::vector<bool>> & board, std::vector<std::string> & lines,
int N, int & num_sol, int cnt = 0, int start_i = 0, int start_j = 0, int depth = 0) {
if (cnt >= N) {
Output(board, lines, false);
// Increase number of solutions.
++num_sol;
return;
}
// Traverse whole board starting from last queen
for (int i = start_i; i < board.size(); ++i)
for (int j = i == start_i ? start_j : 0; j < board[i].size(); ++j) {
bool attacked = false;
// k-loop checks if position [i][j] is being attacked
for (int k = 0; k < (board.size() > board[i].size() ?
board.size() : board[i].size()); ++k)
if (
// Is there horizontal attack
k < board[i].size() && k != j && board[i][k] ||
// Is there vertical attack
k < board.size() && k != i && board[k][j] ||
// Is there main diagonal attack
k < board.size() && k != i && 0 <= j - i + k &&
j - i + k < board[i].size() && board[k][j - i + k] ||
// Is there secondary diagonal attack
k < board.size() && k != i && 0 <= j + i - k &&
j + i - k < board[i].size() && board[k][j + i - k]
) {
attacked = true;
break;
}
if (attacked)
continue;
// Position [i][j] is not under attack, hence placing a queen
board[i][j] = true;
// Recursive descend to place another queen
Solve(board, lines, N, num_sol, cnt + 1, i, j + 1, depth + 1);
// Backtrack, to delete previous queen
board[i][j] = false;
}
if (depth == 0)
Output(board, lines, true);
}
// Function of outputting solutions to console
void Output(std::vector<std::vector<bool>> & board, std::vector<std::string> & lines, bool last) {
if (1) {
if (!last) {
for (int i = 0; i < board.size(); ++i) {
for (int j = 0; j < board[i].size(); ++j)
lines[i].push_back(board[i][j] ? 'Q' : '.');
lines[i] += "|";
}
}
if (lines.at(0).size() >= 70 || last && !lines.at(0).empty()) {
for (int i = 0; i < lines.size(); ++i)
std::cout << lines[i] << std::endl;
for (int j = 0; j < lines.at(0).size(); ++j)
std::cout << (lines.at(0)[j] == '|' ? '+' : '-');
std::cout << std::endl;
lines.clear();
lines.resize(board.size());
}
}
}
int main() {
// rows - number of rows in a board, cols - number of columns in a board
// N - number of queens to be placed
int const rows = 8, cols = 8, N = 8;
// Filling with empty values board [rows][cols]
std::vector<std::vector<bool>> board(rows, std::vector<bool>(cols));
std::vector<std::string> lines(rows);
// Answer, number of solutions
int num_sol = 0;
// Starting a backtracking
Solve(board, lines, N, num_sol);
// Outputting answer
std::cout << "Number of solutions: " << num_sol << std::endl;
}
Advanced:
Try it online!
#include <iostream>
#include <string>
#define MAX(a, b) ((a) >= (b) ? (a) : (b))
enum { max_rows = 32, max_cols = 32, max_max_rows_cols = MAX(max_rows, max_cols) };
void Output(bool (& board)[max_rows][max_cols], std::string (& lines)[max_rows],
int rows, int cols, bool last);
void Solve(bool (& board)[max_rows][max_cols], std::string (& lines)[max_rows],
bool (& busy_cols)[max_cols], bool (& busy_diagA)[2 * max_max_rows_cols],
bool (& busy_diagB)[2 * max_max_rows_cols],
int rows, int cols, int N, int & num_sol, int cnt = 0, int start_i = 0, int depth = 0) {
if (cnt >= N) {
Output(board, lines, rows, cols, false);
++num_sol;
return;
}
int const max_rows_cols = MAX(rows, cols);
if (rows - start_i < N - cnt)
return;
int avail_cols[max_cols];
int avail_cols_cnt = 0;
for (int j = 0; j < cols; ++j)
if (!busy_cols[j]) {
avail_cols[avail_cols_cnt] = j;
++avail_cols_cnt;
}
if (avail_cols_cnt < N - cnt)
return;
for (int i = start_i; i < rows; ++i)
for (int jj = 0; jj < avail_cols_cnt; ++jj) {
int const j = avail_cols[jj];
if (busy_diagA[max_rows_cols + j - i] || busy_diagB[j + i])
continue;
board[i][j] = true;
busy_cols[j] = true;
busy_diagA[max_rows_cols + j - i] = true;
busy_diagB[j + i] = true;
Solve(board, lines, busy_cols, busy_diagA, busy_diagB,
rows, cols, N, num_sol, cnt + 1, i + 1, depth + 1);
board[i][j] = false;
busy_cols[j] = false;
busy_diagA[max_rows_cols + j - i] = false;
busy_diagB[j + i] = false;
}
if (depth == 0)
Output(board, lines, rows, cols, true);
}
void Output(bool (& board)[max_rows][max_cols], std::string (& lines)[max_rows],
int rows, int cols, bool last) {
if (1) {
if (!last) {
for (int i = 0; i < rows; ++i) {
for (int j = 0; j < cols; ++j)
lines[i].push_back(board[i][j] ? 'Q' : '.');
lines[i] += "|";
}
}
if (lines[0].size() >= 70 || last && !lines[0].empty()) {
for (int i = 0; i < rows; ++i)
std::cout << lines[i] << std::endl;
for (int j = 0; j < lines[0].size(); ++j)
std::cout << (lines[0][j] == '|' ? '+' : '-');
std::cout << std::endl;
for (int i = 0; i < rows; ++i)
lines[i].clear();
}
}
}
int main() {
int const rows = 8, cols = 8, N = 8;
bool board[max_rows][max_cols] = {};
std::string lines[max_rows] = {};
bool busy_cols[max_cols] = {};
bool busy_diagA[2 * max_max_rows_cols] = {};
bool busy_diagB[2 * max_max_rows_cols] = {};
int num_sol = 0;
Solve(board, lines, busy_cols, busy_diagA, busy_diagB, rows, cols, N, num_sol);
std::cout << "Number of solutions: " << num_sol << std::endl;
}
Output:
Q.......|Q.......|Q.......|Q.......|.Q......|.Q......|.Q......|.Q......|
....Q...|.....Q..|......Q.|......Q.|...Q....|....Q...|....Q...|.....Q..|
.......Q|.......Q|...Q....|....Q...|.....Q..|......Q.|......Q.|Q.......|
.....Q..|..Q.....|.....Q..|.......Q|.......Q|Q.......|...Q....|......Q.|
..Q.....|......Q.|.......Q|.Q......|..Q.....|..Q.....|Q.......|...Q....|
......Q.|...Q....|.Q......|...Q....|Q.......|.......Q|.......Q|.......Q|
.Q......|.Q......|....Q...|.....Q..|......Q.|.....Q..|.....Q..|..Q.....|
...Q....|....Q...|..Q.....|..Q.....|....Q...|...Q....|..Q.....|....Q...|
--------+--------+--------+--------+--------+--------+--------+--------+
.Q......|.Q......|.Q......|.Q......|..Q.....|..Q.....|..Q.....|..Q.....|
.....Q..|......Q.|......Q.|.......Q|Q.......|....Q...|....Q...|....Q...|
.......Q|..Q.....|....Q...|.....Q..|......Q.|.Q......|.Q......|......Q.|
..Q.....|.....Q..|.......Q|Q.......|....Q...|.......Q|.......Q|Q.......|
Q.......|.......Q|Q.......|..Q.....|.......Q|Q.......|.....Q..|...Q....|
...Q....|....Q...|...Q....|....Q...|.Q......|......Q.|...Q....|.Q......|
......Q.|Q.......|.....Q..|......Q.|...Q....|...Q....|......Q.|.......Q|
....Q...|...Q....|..Q.....|...Q....|.....Q..|.....Q..|Q.......|.....Q..|
--------+--------+--------+--------+--------+--------+--------+--------+
..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|
....Q...|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|
.......Q|.Q......|.Q......|.Q......|...Q....|...Q....|.......Q|.......Q|
...Q....|....Q...|......Q.|......Q.|Q.......|.Q......|Q.......|Q.......|
Q.......|.......Q|Q.......|....Q...|.......Q|.......Q|...Q....|....Q...|
......Q.|Q.......|...Q....|Q.......|....Q...|....Q...|......Q.|......Q.|
.Q......|......Q.|.......Q|.......Q|......Q.|......Q.|....Q...|.Q......|
.....Q..|...Q....|....Q...|...Q....|.Q......|Q.......|.Q......|...Q....|
--------+--------+--------+--------+--------+--------+--------+--------+
..Q.....|..Q.....|..Q.....|..Q.....|...Q....|...Q....|...Q....|...Q....|
.....Q..|......Q.|......Q.|.......Q|Q.......|Q.......|.Q......|.Q......|
.......Q|.Q......|.Q......|...Q....|....Q...|....Q...|....Q...|......Q.|
.Q......|.......Q|.......Q|......Q.|.......Q|.......Q|.......Q|..Q.....|
...Q....|....Q...|.....Q..|Q.......|.Q......|.....Q..|.....Q..|.....Q..|
Q.......|Q.......|...Q....|.....Q..|......Q.|..Q.....|Q.......|.......Q|
......Q.|...Q....|Q.......|.Q......|..Q.....|......Q.|..Q.....|Q.......|
....Q...|.....Q..|....Q...|....Q...|.....Q..|.Q......|......Q.|....Q...|
--------+--------+--------+--------+--------+--------+--------+--------+
...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|
.Q......|.Q......|.Q......|.Q......|.....Q..|.....Q..|.....Q..|......Q.|
......Q.|......Q.|.......Q|.......Q|Q.......|.......Q|.......Q|Q.......|
..Q.....|....Q...|....Q...|.....Q..|....Q...|.Q......|..Q.....|.......Q|
.....Q..|Q.......|......Q.|Q.......|.Q......|......Q.|Q.......|....Q...|
.......Q|.......Q|Q.......|..Q.....|.......Q|Q.......|......Q.|.Q......|
....Q...|.....Q..|..Q.....|....Q...|..Q.....|..Q.....|....Q...|.....Q..|
Q.......|..Q.....|.....Q..|......Q.|......Q.|....Q...|.Q......|..Q.....|
--------+--------+--------+--------+--------+--------+--------+--------+
...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|....Q...|....Q...|
......Q.|......Q.|......Q.|.......Q|.......Q|.......Q|Q.......|Q.......|
..Q.....|....Q...|....Q...|Q.......|Q.......|....Q...|...Q....|.......Q|
.......Q|.Q......|..Q.....|..Q.....|....Q...|..Q.....|.....Q..|...Q....|
.Q......|.....Q..|Q.......|.....Q..|......Q.|Q.......|.......Q|.Q......|
....Q...|Q.......|.....Q..|.Q......|.Q......|......Q.|.Q......|......Q.|
Q.......|..Q.....|.......Q|......Q.|.....Q..|.Q......|......Q.|..Q.....|
.....Q..|.......Q|.Q......|....Q...|..Q.....|.....Q..|..Q.....|.....Q..|
--------+--------+--------+--------+--------+--------+--------+--------+
....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|
Q.......|.Q......|.Q......|.Q......|.Q......|..Q.....|..Q.....|..Q.....|
.......Q|...Q....|...Q....|.....Q..|.......Q|Q.......|Q.......|.......Q|
.....Q..|.....Q..|......Q.|Q.......|Q.......|.....Q..|......Q.|...Q....|
..Q.....|.......Q|..Q.....|......Q.|...Q....|.......Q|.Q......|......Q.|
......Q.|..Q.....|.......Q|...Q....|......Q.|.Q......|.......Q|Q.......|
.Q......|Q.......|.....Q..|.......Q|..Q.....|...Q....|.....Q..|.....Q..|
...Q....|......Q.|Q.......|..Q.....|.....Q..|......Q.|...Q....|.Q......|
--------+--------+--------+--------+--------+--------+--------+--------+
....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|
......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|.......Q|.......Q|
Q.......|Q.......|.Q......|.Q......|.Q......|...Q....|...Q....|...Q....|
..Q.....|...Q....|...Q....|.....Q..|.....Q..|Q.......|Q.......|Q.......|
.......Q|.Q......|.......Q|..Q.....|..Q.....|..Q.....|..Q.....|......Q.|
.....Q..|.......Q|Q.......|Q.......|Q.......|.......Q|.....Q..|.Q......|
...Q....|.....Q..|..Q.....|...Q....|.......Q|.....Q..|.Q......|.....Q..|
.Q......|..Q.....|.....Q..|.......Q|...Q....|.Q......|......Q.|..Q.....|
--------+--------+--------+--------+--------+--------+--------+--------+
.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|
Q.......|.Q......|.Q......|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|
....Q...|......Q.|......Q.|Q.......|Q.......|Q.......|....Q...|....Q...|
.Q......|Q.......|Q.......|......Q.|.......Q|.......Q|......Q.|.......Q|
.......Q|..Q.....|...Q....|....Q...|...Q....|....Q...|Q.......|Q.......|
..Q.....|....Q...|.......Q|.......Q|.Q......|.Q......|...Q....|...Q....|
......Q.|.......Q|....Q...|.Q......|......Q.|...Q....|.Q......|.Q......|
...Q....|...Q....|..Q.....|...Q....|....Q...|......Q.|.......Q|......Q.|
--------+--------+--------+--------+--------+--------+--------+--------+
.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|
..Q.....|..Q.....|..Q.....|...Q....|...Q....|...Q....|...Q....|.......Q|
......Q.|......Q.|......Q.|Q.......|.Q......|......Q.|......Q.|.Q......|
.Q......|.Q......|...Q....|....Q...|.......Q|Q.......|Q.......|...Q....|
...Q....|.......Q|Q.......|.......Q|....Q...|..Q.....|.......Q|Q.......|
.......Q|....Q...|.......Q|.Q......|......Q.|....Q...|.Q......|......Q.|
Q.......|Q.......|.Q......|......Q.|Q.......|.Q......|....Q...|....Q...|
....Q...|...Q....|....Q...|..Q.....|..Q.....|.......Q|..Q.....|..Q.....|
--------+--------+--------+--------+--------+--------+--------+--------+
......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|
Q.......|.Q......|.Q......|..Q.....|..Q.....|...Q....|...Q....|....Q...|
..Q.....|...Q....|.....Q..|Q.......|.......Q|.Q......|.Q......|..Q.....|
.......Q|Q.......|..Q.....|.....Q..|.Q......|....Q...|.......Q|Q.......|
.....Q..|.......Q|Q.......|.......Q|....Q...|.......Q|.....Q..|.....Q..|
...Q....|....Q...|...Q....|....Q...|Q.......|Q.......|Q.......|.......Q|
.Q......|..Q.....|.......Q|.Q......|.....Q..|..Q.....|..Q.....|.Q......|
....Q...|.....Q..|....Q...|...Q....|...Q....|.....Q..|....Q...|...Q....|
--------+--------+--------+--------+--------+--------+--------+--------+
.......Q|.......Q|.......Q|.......Q|
.Q......|.Q......|..Q.....|...Q....|
...Q....|....Q...|Q.......|Q.......|
Q.......|..Q.....|.....Q..|..Q.....|
......Q.|Q.......|.Q......|.....Q..|
....Q...|......Q.|....Q...|.Q......|
..Q.....|...Q....|......Q.|......Q.|
.....Q..|.....Q..|...Q....|....Q...|
--------+--------+--------+--------+
Number of solutions: 92
There are several issues, starting from the multiple memory leaks (see e.g. the empty destructor or the delete[] boardPtr; at the beginning of ChessBoard::setSize), but what prevents the program to solve the problem is this:
bool ChessBoard::canPlace(char** boardPtr, int row, int column)
{
int i, j;
// Check row
for (i = 0; i < column; i++)
if (boardPtr[row][i] )
// ^^^^^^^^^^^^^^^^
return false;
// ...
}
That condition and the following ones should be boardPtr[row][i] == 'Q', because, as written, it just check if the char is not 0, while an empty spot is indicated by a . in this program.
I have coded up a gauss seidel method that works just fine but i cannot seem to figure out how to convert that to jacobi... I know it should be easy so i must be missing something simple. For the assignment i had to make my own vector and matrix classes so that is why Vector is capital and called differently. Here is my working gauss seidel code:
else if (mode == 3) {
Vector temp;
temp.allocateData(b.numElems());
Vector old = temp;
Vector sum;
double f = 50;
int y = 4;
double tol = 1e-12;
double error = 10;
int max = 999999;
int count = 0;
while ( error > tol && max > count) {
for (int i = 0; i < row_; i++) {
temp.setVal(i, b.getVal(i) / M[i][i]);
for (int j = 0; j < col_; j++) {
if (j == i) {
continue;
}
temp.setVal(i, temp.getVal(i) - ((M[i][j] / M[i][i]) * temp.getVal(j)));
old.setVal(j, temp.getVal(i));
}
cout<<"x"<< i + 1 << "="<< temp.getVal(i) <<" \n";
error = abs(temp.getVal(i)-old.getVal(i))/abs(temp.getVal(i));
old = temp;
}
cout << "\n";
count++;
}
}
and here is my attempt at jacobi:
else if (mode == 2) {
Vector temp;
temp.allocateData(b.numElems());
Vector old = temp;
Vector sum;
double f = 50;
int y = 4;
double tol = 1e-12;
double error = 10;
int max = 999999;
int count = 0;
while ( error > tol && max > count) {
old.allocateData(b.numElems());
for (int i = 0; i < row_; i++) {
old.setVal(i, temp.getVal(i));
temp.setVal(i, b.getVal(i) / M[i][i]);
for (int j = 0; j < col_; j++) {
if (j == i) {
continue;
}
temp.setVal(i, temp.getVal(i) - ((M[i][j] / M[i][i]) * old.getVal(j)));
}
cout<<"x"<< i + 1 << "="<< temp.getVal(i) <<" \n";
error = abs(temp.getVal(i)-old.getVal(i))/abs(temp.getVal(i));
}
cout << "\n";
count++;
}
}
thanks everyone ahead of time for the help!!!
Alright so I have created this code. However, when i run it, it stops when it displays 104 for the counter??? I am so frustrated because I don't know how this could happen. The purpose of the code is to do the typical magic number output where the rows all add up to the same thing, the columns all add up to the same thing, and the diaganols all add up to the same thing. I believe the functions to do these calculations are correct, but the counter keeps stopping short of the 10000 attempts I am trying to do.
#include <iostream>
#include<time.h>
#include<stdlib.h>
using namespace std;
void getrandom();
void insertnumber(int n);
bool magic();
void create();
const int rows = 3;
const int cols = 3;
int arr[rows][cols] = { {0,0,0}, {0,0,0} , {0,0,0} };
int main() {
int counter = 0;
do
{
counter++;
cout << counter << endl;
getrandom();
if (counter == 100000)
break;
} while (!magic());
create();
cout << "It took " << counter << " tries." << endl;
return 0;
}
void getrandom() {
int n = 0;
const int size = 9;
int oldnum[size];
for (int i = 0; i < rows * cols; i++) {
oldnum[i] = 0;
}
srand(time(NULL)); // had to import the new libraries to use this
bool used = true;
for (int i = 0; i < size; i++) {
do
{
used = true;
n = rand() % 9 + 1;
if (oldnum[n - 1] == 0)
{
oldnum[n - 1] = n;
used = false;
}
} while (used);
insertnumber(n);
}
}
void insertnumber(int n) {
for (int i = 0; i < rows; i++) {
for (int j = 0; i < cols; j++) {
if (arr[i][j] == 0) {
arr[i][j] = n;
return;
}
}
}
}
bool magic() {
int rowsum = arr[0][0] + arr[0][1] + arr[0][2];
for (int i = 1; i < cols; i++)
{
if (arr[i][0] + arr[i][1] + arr[i][2] != rowsum)
return false;
}
for (int j = 0; j < rows; j++)
{
if (arr[0][j] + arr[1][j] + arr[2][j] != rowsum)
return false;
}
if (arr[0][0] + arr[1][1] + arr[2][2] != rowsum)
return false;
if (arr[0][2] + arr[1][1] + arr[2][0] != rowsum)
return false;
return true;
}
void create() {
{
for (int i = 0; i < rows; i++) {
for (int j = 0; i < cols; j++) {
cout << arr[i][j] << " ";
}
cout << endl;
}
}
}
You can try using a debugger for such problems.
I think you code crashes because of this:
for (int i = 0; i < rows; i++) {
for (int j = 0; i < cols; j++) {
It looks like you mean j < cols here :)
Check line 76. When I compile and run the code, line 76 is where the exception is thrown.
This line specifically
arr[i][j] = n;
It seems your insertnumber() function is the culprit.
I am trying to create a simulation of conway's game of life.
I keep getting a "vector subscript out of range" error after about 300 generation and I don't understand the reason. From what I could gather it's caused by using an invalid index. The most likely section is the first part of the draw function where I find empty rows and replace them with "\n" to save time.
I've started learning to code not too long ago so I may be making baby mistakes.
Edit: visual studio point the error after the third for loop in the frame function, on if (emptyRows[m] == i)
Here's the full code :
#include <array>
#include <time.h>
#include <vector>
const int WIDTH = 150;
const int HEIGHT = 50;
bool table[WIDTH][HEIGHT];
bool tableNew[WIDTH][HEIGHT];
std::string buffer;
int total;
int counter = 0;
std::vector<int> emptyRows;
int numberOfNeighbours(int Y, int X) {
if (X == 0 || Y == 0 || X == WIDTH || Y == HEIGHT)
return 2;
total = 0;
for (int i = -1; i < 2; i++) {
for (int j = -1; j < 2; j++) {
if (table[X + j][Y + i] == true)
total++;
}
}
total -= table[X][Y];
return total;
}
void draw() {
srand((int)time(0));
int m = 0;
bool check = 0;
for (int i = 0; i < HEIGHT; i++) {
for (int j = 0; j < WIDTH; j++) {
if (table[j][i] == 1)
check = 1;
}
if (check == 0)
emptyRows.push_back(i);
else
check = 0;
}
for (int i = 0; i < HEIGHT; i++) {
if (emptyRows.size() >= 1) {
if (emptyRows[m] == i) {
buffer.append("\n");
m++;
continue;
}
}
for (int j = 0; j < WIDTH; j++) {
if (table[j][i] == 1) buffer.push_back('#');
else buffer.push_back(' ');
}
buffer.append("\n");
}
std::cout << buffer;
std::cout << std::endl << "Generazione numero:" << counter;
emptyRows.erase(emptyRows.begin(), emptyRows.end());
buffer.erase(buffer.begin(), buffer.end());
m = 0;
}
void reset() {
for (int i = 0; i < HEIGHT; i++) {
for (int j = 0; j < WIDTH; j++) {
table[j][i] = tableNew[j][i];
}
}
}
void logic() {
for (int i = 0; i < HEIGHT; i++) {
for (int j = 0; j < WIDTH; j++) {
int k = numberOfNeighbours(i, j);
if (table[j][i] == 0 && k == 3)
tableNew[j][i] = 1;
else if (table[j][i] == 1 && k != 2 && k != 3)
tableNew[j][i] = 0;
else
tableNew[j][i] = table[j][i];
}
}
}
int main(){
for (int i = 0; i < HEIGHT; i++) {
for (int j = 0; j < WIDTH; j++) {
if ((rand() % 2) == 1)
table[j][i] = 1;
}
}
while (true) {
counter++;
draw();
logic();
reset();
system("cls");
}
return 0;
}
I have to calculate the values of a hot plate and have it accurate only to the first decimal place. I am stumped on trying to figure out how to check all the array values if they changed. I found out that 724 runs made no change after that to the 4th decimal (how many were being printed).
Is there a way to compare doubles variables only up to the n-th decimal place?
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
const int ARRAY_SIZE = 20;
const int NEIGHBORS = 4;
void initialize(double hot_plate[][ARRAY_SIZE]);
bool writeFile(const double HOT_PLATE[][ARRAY_SIZE],
const string FILE_NAME);
double sum_cell(const double HOT_PLATE[][ARRAY_SIZE],
const int CELL_X, const int CELL_Y);
int main()
{
double hot_plate[ARRAY_SIZE][ARRAY_SIZE];
initialize(hot_plate);
string file_name = "hot_plate.csv";
//accuracy up to 4 decmials
int runs = 724;
while ( runs > 0)
{
for (int i = 0; i < ARRAY_SIZE; i++)
{
for (int j = 0; j < ARRAY_SIZE; j++)
{
if (i > 0 && i < ARRAY_SIZE - 1 && j > 0 && j < ARRAY_SIZE - 1)
{
hot_plate[i][j] = sum_cell(hot_plate, j, i);
}
}
}
runs--;
}
if (writeFile(hot_plate, file_name))
{
cout << "File wrote correctly\n";
}
else
{
cout << "The file did not write!\n";
}
//system("pause");
return 0;
}
////////////////////////////////////////////////////////////////////////////////
//////////////////////////// Completed Code ////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
double sum_cell(const double HOT_PLATE[][ARRAY_SIZE],
const int CELL_X, const int CELL_Y)
{
/* This code should never go out of bounds as it's in an if statement
if (i > 0 && i < ARRAY_SIZE - 1 && j > 0 && j < ARRAY_SIZE - 1)
*/
double cell_num = HOT_PLATE[CELL_X - 1][CELL_Y]; // Top
cell_num += HOT_PLATE[CELL_X][CELL_Y - 1]; // Left
cell_num += HOT_PLATE[CELL_X][CELL_Y + 1]; // Right
cell_num += HOT_PLATE[CELL_X + 1][CELL_Y]; // Bottom
cell_num /= NEIGHBORS;
return cell_num;
}
// setup the Array so all values are defined when starting
void initialize(double hot_plate[][ARRAY_SIZE])
{
for (int i = 0; i < ARRAY_SIZE; i++)
{
for (int j = 0; j < ARRAY_SIZE; j++)
{
if (i == 0 || i == ARRAY_SIZE - 1)
{
if (j == 0 || j == ARRAY_SIZE - 1)
{
hot_plate[i][j] = 0.0;
}
else
{
hot_plate[i][j] = 100.0;
}
}
else
{
hot_plate[i][j] = 0.0;
}
}
}
}
// Write the data to the CSV file
bool writeFile(const double HOT_PLATE[][ARRAY_SIZE],
const string FILE_NAME)
{
// open the file
ofstream fout(FILE_NAME);
if (fout.fail())
return false;
for (int i = 0; i < ARRAY_SIZE; i++)
{
for (int j = 0; j < ARRAY_SIZE; j++)
{
fout << HOT_PLATE[i][j];
if ( j < ARRAY_SIZE - 1)
{
fout << ", ";
}
else if (i != ARRAY_SIZE - 1)
{
fout << endl;
}
}
}
// close the input stream from the file.
fout.close();
return true;
}
Is there a way to compare doubles variables only up to the n-th decimal place?
Yes there is, check whether the absolute value of the difference between them is less than 10^-n.
Check comparing floating point numbers and this post on deniweb.
With this function
double getUpToDecPlace (double value, int decPlace)
{
int dec = 1;
for (int i = 0; i < decPlace; i++)
{
dec *= 10;
}
return floor(value*dec + 0.5)/dec;
}
which would return 12.35 for getUpToDecPlace(12.345678, 2), you can compare doubles up to an arbitrary decimal place:
double var1 = 12.345678;
double var2 = 12.351234;
bool comp1 = (getUpToDecPlace(var1, 2) == getUpToDecPlace(var2, 2)); // true
bool comp2 = (getUpToDecPlace(var1, 3) == getUpToDecPlace(var2, 3)); // false
There are so many problems here.
You are updating the hot_plate array in-place. So some of the values you use from the 'previous generation' have already been updated in the current generation! You have to compute each generation in a separate array, and then copy it back to the 'master' hot_plate array.
If you want the final result accurate in the first decimal place, it's not enough to continue until the values don't change by more than 0.1. For instance, some values might change by more than 0.05 for ten more generations, which would amount to a change of more than 0.5. In fact, this is a very tricky issue: it requires a global analysis of how the initial conditions evolve over time.
Are you sure you have sum_cell right? The temperature of hot_plate[i][j] at the next generation should surely depend on the current value of hot_plate[i][j], and not just on its neighbours?
Also, this looks a bit silly:
for (int i = 0; i < ARRAY_SIZE; i++)
{
for (int j = 0; j < ARRAY_SIZE; j++)
{
if (i > 0 && i < ARRAY_SIZE - 1 && j > 0 && j < ARRAY_SIZE - 1)
I suggest the equivalent formulation:
for (int i = 1; i < ARRAY_SIZE - 1; i++)
{
for (int j = 1; j < ARRAY_SIZE - 1; j++)
As for testing equality to the nth decimal place, other posters have covered that.
Store the measured FP value as a scaled integer:
ix = int(fp * 10000)
You can then do direct comparisons with the required precision.