Question

I have been staring at this code for few hours, tried walkthrough,debugging with autos and breakpoints and it’s no solution so far. Maybie someone’s fresh look would help me 😉 .

#include <iostream>

using namespace std;

int matrix[9][9] = {{0, 0, 6, 0, 0, 0, 1, 0, 5},
                    {0, 4, 0, 7, 0, 6, 0, 3, 9},
                    {2, 0, 0, 9, 3, 0, 6, 0, 0},
                    {7, 0, 0, 1, 8, 0, 5, 0, 4},
                    {0, 0, 4, 0, 6, 0, 9, 0, 0},
                    {1, 0, 9, 0, 5, 2, 0, 0, 3},
                    {0, 0, 1, 0, 9, 3, 0, 0, 7},
                    {6, 7, 0, 5, 0, 8, 0, 9, 0},
                    {9, 0, 8, 0, 0, 0, 4, 0, 0}};


bool check(int column  ,int row,int checkedValue) 
{
    //column check
    for(int i=0; i<9; i++) 
    {       
        if(i==row)continue;

        if(checkedValue==matrix[column][i]) return false;
    }
    //row check 
    for(int i=0; i<9; i++) 
    {   
        if(i==column) continue;
        if(checkedValue==matrix[i][row]) return false;
    }                       
        return true;
}   



int main()
{
    cout<<check(4,0,4); //Why does it output 0? There is no "4" in the 5th column and the 1st row.

    system("pause");
    return 0;
}

The function check(column,row,value) was designed to return 0 when number occurs at least once in the “matrix” two dimensional table. This program is a chunk of sudoku solver.

Answer 1

You mixed the indices up in the if statements. They should be:

if(checkedValue==matrix[i][column]) return false; // not matrix[column][i]

and

if(checkedValue==matrix[row][i]) return false;    // not matrix[i][row]

The reason is that the first dimension is the row. You can check this by printing matrix[2][0].
For your matrix, you will get 2 (and not 6).