Sudoku Solver in c++

#include <bits/stdc++.h> using namespace std; int arr[9][9]; bool isSafeRow(int row, int value) { for (int i = 0; i < 9; ++i) { if(arr[row][i]==value) return true; } return false; } bool isSafeColumn(int col, int value) { for (int i = 0; i < 9; ++i) { if(arr[i][col]==value) return true; } return false; } bool isSafeBox(int startRow, int startCol, int value) { for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) { if (arr[startRow+i][startCol+j]==value) { return true; } } } return false; } bool isSafe(int row, int col, int value) { return !isSafeRow(row,value) && !isSafeColumn(col,value) && !isSafeBox(row-row%3,col-col%3,value); } bool sudoku() { int row,col; int flag = 0; for (int i = 0; i < 9; ++i) { for (int j = 0; j < 9; ++j) { if (arr[i][j]==0) { row = i; col = j; flag = 1; //printf("Test1...\n"); break; } } if (flag) { break; } } if (!flag) { return true; } /*if(!unassignedLocation(row,col)) { return true; }*/ //printf("%d %d\n",row,col); for (int digit = 1; digit <= 9; ++digit) { //printf("New... %d\n",isSafe(row,col,digit)); if(isSafe(row,col,digit)) { //printf("Test\n"); arr[row][col] = digit; if(sudoku()) return true; arr[row][col] = 0; } } return false; } int main() { while(1) { printf("Enter (-1,-1,-1) to quit otherwise enter index i,j,value\n"); int i,j,value; scanf("%d%d%d",&i,&j,&value); if(i==-1 || j==-1 || value==-1) { break; } arr[i][j] = value; } if(sudoku()) { for (int i = 0; i < 9; ++i) { for (int j = 0; j < 9; ++j) { printf("%2d ",arr[i][j]); } printf("\n"); } } else { printf("No Solution Exist\n"); } }