sudoku solver

#include <bits/stdc++.h>
using namespace std;
///****************
const int n = 9, bn = 3;
int sudokuGrid[n + 2][n + 2];

bool usedInRow(int row, int num) {
    for (int i = 0; i < n; i++)
        if (sudokuGrid[row][i] == num)
            return true;
    return false;
}

bool usedInCol(int col, int num) {
    for (int i = 0; i < n; i++)
        if (sudokuGrid[i][col] == num)
            return true;
    return false;
}

bool usedInBox(int bsRow, int bsCol, int num) {
    for (int i = bsRow; i < bsRow + bn; i++)
        for (int j = bsCol; j < bsCol + bn; j++) {
            if (sudokuGrid[i][j] == num) {
                return true;
            }
        }
    return false;
}

bool isSafe(int row, int col, int num) {
    bool e = !usedInRow(row, num);
    e = e && !usedInCol(col, num);
    e = e && !usedInBox(row - row % bn,
                        col - col % bn,
                        num);
    return e;
}

bool findEmptyPlace(int &row, int &col) {
    for (row = 0; row < n; row++)
        for (col = 0; col < n; col++)
            if (!sudokuGrid[row][col])
                return true;
    return false;
}

bool solveSudoku() {
    int row, col;
    if (!findEmptyPlace(row, col))
        return true;
    for (int num = 1; num <= n; num++) {
        if (isSafe(row, col, num)) {
            sudokuGrid[row][col] = num;
            if (solveSudoku())
                return true;
            sudokuGrid[row][col] = 0;
        }
    }
    return false;
}

void read() {
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            cin >> sudokuGrid[i][j];
}

void display(bool ok) {
    if (!ok) {
        puts("IMPOSSIBLE!");
        return;
    }
    cout << string(17, '-') << endl;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++)
            cout << sudokuGrid[i][j] << ' ';
        puts("");
    }
}

int main()
{
    read();
    display(solveSudoku());
    return 0;
}