Program to check the numbers possible at a position of a Sudoku.

sudoku_checker.cpp

//This program checks the numbers possible at a position of a Sudoku.
//@author : Rohit Gupta
#include <iostream>

using namespace std;

int main() {
	int i, j, p, q, ch = 1, freq[10] = {0};
	int s[9][9] = {
		{0, 0, 0, 0, 0, 0, 6, 8, 0},
		{0, 0, 0, 0, 7, 3, 0, 0, 9},
		{3, 0, 9, 0, 0, 0, 0, 4, 5},
		{4, 9, 0, 0, 0, 0, 0, 0, 0},
		{8, 0, 3, 0, 5, 0, 9, 0, 2},
		{0, 0, 0, 0, 0, 0, 0, 3, 6},
		{9, 6, 0, 0, 0, 0, 3, 0, 8},
		{7, 0, 0, 6, 8, 0, 0, 0, 0},
		{0, 2, 8, 0, 0, 0, 0, 0, 0}
	};
	
	while(ch==1) {
		cout<<"Enter positions(row, col): ";
		cin>>i>>j;
		
		if(i<1 || i>9 || j<1 || j>9) {
			cout<<"\nErr! Please enter values in range(i.e within 1 and 9). Try again!\n"<<endl; 
			continue;
		}
		
		i--; j--;
		
		if(s[i][j]>0) {
			cout<<"\nErr! This position is already filled. Try Again!\n"<<endl;
			continue;
		}
		
		for(p=0; p<9; p++){
			if(p==i) continue;
			freq[s[p][j]]++;
		}
		
		for(q=0; q<9; q++) {
			if(q==j) continue;
			freq[s[i][q]]++;
		}
		
		for(p=i-(i-1)%3; p<= i+(3-i%3)%3; p++) {
			for(q=i-(i-1)%3; q<= i+(3-i%3)%3; q++) {
				if(p==i && q==j) continue;
				freq[s[p-1][q-1]]++;
			}
		}
		
		cout<<"\nPossible numbers on position ("<<++i<<", "<<++j<<") is: ";
		
		for(p=1; p<10; p++) {
			if(freq[p]<1){
				cout<<p<<" ";
			}
		}
		
		cout<<"\n\nTo check again press '1' or anything to quit.: ";
		cin>>ch;
		cout<<endl;
	}
    return 0;
}