Hi, I am making program that finds solution how to put 12 knights(horses) to chess board that every square is dominated or engaged by other knight.
Look at my code:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>



//(*******************************************************************************)
void addNulls(char L[][9], int N[], int M[])
{
    int i,j,g;

    for (i=1 ; i<9 ; i++)
        for (j=1 ; j<9 ; j++)
            if (L[i][j]!='K')
                L[i][j]='0';
    for (i=1 ; i <9 ; i++)
        for (j=1 ; j <9; j++)
            if (L[i][j]=='K')
                for (g=1 ; g <9; g++)
                    if (i+N[g]>0&&i+N[g]<9 && j+M[g]>0 && j+M[g]<9 && L[i+N[g]][ j+M[g]] == '0')
                        L[i+N[g]][ j+M[g]] = '*';
}
//(*******************************************************************************)
bool checkIf(char L[][9], int N[], int M[])
{
    int i, j;

    for ( i=1 ; i<9; i++)
        for (j=1 ; j <9; j++)
            if (L[i][j]=='K')
            {
                if (i-2>0)
                {
                    if (j-1>0 && L[i-2][j-1]=='0')
                        L[i-2][j-1]='*';
                    if (j+1<9 && L[i-2][j+1]=='0')
                        L[i-2][j+1]='*';
                    if (j-2>0 && L[i-1][j-2]=='0')
                        L[i-1][j-2]='*';
                    if (j+2<9 && L[i-1][j+2]=='0')
                        L[i-1][j+2]='*';
                }
                else if (i-1>0)
                {
                    if (j-2>0 && L[i-1][j-2]=='0')
                        L[i-1][j-2]='*';
                    if (j+2<9 && L[i-1][j+2]=='0')
                        L[i-1][j+2]='*';
                }
                if (i+2<9)
                {
                    if (j-1>0 && L[i+2][j-1]=='0')
                        L[i+2][j-1]='*';
                    if (j+1<9 && L[i+2][j+1]=='0')
                        L[i+2][j+1]='*';
                    if (j-2>0 && L[i+1][j-2]=='0')
                        L[i+1][j-2]='*';
                    if (j+2<9 && L[i+1][j+2]=='0')
                        L[i+1][j+2]='*';
                }
                else if (i+1<9)
                {
                    if (j-2>0 && L[i+1][j-2]=='0')
                        L[i+1][j-2]='*';
                    if (j+2<9 && L[i+1][j+2]=='0')
                        L[i+1][j+2]='*';
                }
            }
    return true;
    for( i=1 ; i<=9; i++)
        for (j=1 ; j<=9; j++)
        {
            if (L[i][j]=='0')
                return false;
        }
}
//(*******************************************************************************)
void printBoard(char L[][9])
{
    int i,j;

    for (i=1 ; i<9 ; i++)
    {
        for (j=1 ; j<9 ; j++)
        {
            printf("%2c|",L[i][j]);
        }
        printf("\n");
        j=1;
    }
}
//(*******************************************************************************)
void modeling(char L[][9], int N[], int M[], int z)
{
    int i,j,o;

    i=1;
    j=1;
    if (z<12)
    {
        while (L[i][j]!='0' && i<9)
        {
            j=j+1;
            if (j==9)
            {
                j=1;
                i=i+1;
            }
        }
        o=1;
        while (o<10)
        {
            if (i+N[o]>0 && j+M[o]>0 && i+N[o]<9 && j+M[o]<9 && L[i+N[o]][j+M[o]]!='K')
            {
                L[i+N[o]][j+M[o]]='K';
                addNulls(L,N,M);
                z=z+1;
                modeling(L,N,M,z);
                if (checkIf(L,N,M)==false)
                {
                    L[i+N[o]][j+M[o]]='0';
                    z=z-1;
                }
                else break;
            }
            o=o+1;
        }
    }
    else
    {

        if (checkIf(L,N,M)==true)
        {

            printBoard(L);

        }
    }
}
//(*******************************************************************************)
main()
{
    char L[9][9]; // chess board
    int N[10],M[10]; //traverses

    N[1]=1;
    M[1]=2;
    N[2]=1;
    M[2]=-2;
    N[3]=2;
    M[3]=-1;
    N[4]=2;
    M[4]=1;
    N[5]=-2;
    M[5]=-1;
    N[6]=-2;
    M[6]=1;
    N[7]=-1;
    M[7]=-2;
    N[8]=-1;
    M[8]=2;
    N[9]=0;
    M[9]=0;
    addNulls(L,N,M);
    modeling(L,N,M,0);
    printf("end");

}

I don't get the right output because there are some not dominated squares left.
Maybe you can spot my mistake?

You would fail my class... :-( DO NOT fail to use curly-braces to delimit ALL conditional statements and loops. This is one of the biggest causes of system logic issues...

Fix that, and I'll take another look at your code.

@rubberman , you mean like this:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>



//(*******************************************************************************)
void addNulls(char L[][9], int N[], int M[])
{
    int i,j,g;

    for (i=1 ; i<9 ; i++)
    {
        for (j=1 ; j<9 ; j++)
        {
            if (L[i][j]!='K')
            {
                L[i][j]='0';
            }
        }
    }
    for (i=1 ; i <9 ; i++)
    {
        for (j=1 ; j <9; j++)
        {
            if (L[i][j]=='K')
            {
                for (g=1 ; g <10; g++)
                {
                    if (i+N[g]>0&&i+N[g]<9 && j+M[g]>0 && j+M[g]<9 && L[i+N[g]][ j+M[g]] == '0')
                    {
                        L[i+N[g]][ j+M[g]] = '*';
                    }
                }
            }
        }
    }
}
//(*******************************************************************************)
bool checkIf(char L[][9], int N[], int M[])
{
    int i, j;

    for ( i=1 ; i<9; i++)
    {
        for (j=1 ; j <9; j++)
        {
            if (L[i][j]=='K')
            {
                if (i-2>0)
                {
                    if (j-1>0 && L[i-2][j-1]=='0')
                    {
                        L[i-2][j-1]='*';
                    }
                    if (j+1<9 && L[i-2][j+1]=='0')
                    {

                        L[i-2][j+1]='*';
                    }
                    if (j-2>0 && L[i-1][j-2]=='0')
                    {
                        L[i-1][j-2]='*';
                    }
                    if (j+2<9 && L[i-1][j+2]=='0')
                    {
                        L[i-1][j+2]='*';
                    }
                }
                else if (i-1>0)
                {
                    if (j-2>0 && L[i-1][j-2]=='0')
                    {
                        L[i-1][j-2]='*';
                    }
                    if (j+2<9 && L[i-1][j+2]=='0')
                    {
                        L[i-1][j+2]='*';
                    }
                }
                if (i+2<9)
                {
                    if (j-1>0 && L[i+2][j-1]=='0')
                    {
                        L[i+2][j-1]='*';
                    }
                    if (j+1<9 && L[i+2][j+1]=='0')
                    {
                        L[i+2][j+1]='*';
                    }
                    if (j-2>0 && L[i+1][j-2]=='0')
                    {
                        L[i+1][j-2]='*';
                    }
                    if (j+2<9 && L[i+1][j+2]=='0')
                    {
                        L[i+1][j+2]='*';
                    }
                    // return true;
                }
                else if (i+1<9)
                {
                    if (j-2>0 && L[i+1][j-2]=='0')
                    {
                        L[i+1][j-2]='*';
                    }
                    if (j+2<9 && L[i+1][j+2]=='0')
                    {
                        L[i+1][j+2]='*';
                    }
                }

            }

        }
        //return true;
    }
    int cnt=0;
    for( i=1 ; i<9; i++)
    {
        for (j=1 ; j<9; j++)
        {

            if (L[i][j]=='0')
            {
                cnt++;
            }


        }
    }
    //printf("%d\n", cnt);
    if(cnt==0) return true;
    else return false;

}
//(*******************************************************************************)
void printBoard(char L[][9])
{
    int i,j;

    for (i=1 ; i<9 ; i++)
    {
        for (j=1 ; j<9 ; j++)
        {
            printf("%2c|",L[i][j]);
        }
        printf("\n");
        j=1;
    }
}
//(*******************************************************************************)
void modeling(char L[][9], int N[], int M[], int z)
{
    int i,j,o;

    i=1;
    j=1;
    if (z<12)
    {
        while (L[i][j]!='0' && i<9)
        {
            j=j+1;
            if (j==9)
            {
                j=1;
                i=i+1;
            }
        }
        o=1;
        while (o<10)
        {
            if (i+N[o]>0 && j+M[o]>0 && i+N[o]<9 && j+M[o]<9 && L[i+N[o]][j+M[o]]!='K')
            {
                L[i+N[o]][j+M[o]]='K';
                addNulls(L,N,M);
                z=z+1;
                modeling(L,N,M,z);
                if (!checkIf(L,N,M))
                {
                    L[i+N[o]][j+M[o]]='0';
                    z=z-1;
                }
                else break;
            }
            o=o+1;
        }
    }
    else
    {

        if (checkIf(L,N,M))
        {

            printBoard(L);

        }
    }
}
//(*******************************************************************************)
main()
{
    char L[9][9]; // chess board
    int N[10],M[10]; //traverses

    N[1]=1;
    M[1]=2;
    N[2]=1;
    M[2]=-2;
    N[3]=2;
    M[3]=-1;
    N[4]=2;
    M[4]=1;
    N[5]=-2;
    M[5]=-1;
    N[6]=-2;
    M[6]=1;
    N[7]=-1;
    M[7]=-2;
    N[8]=-1;
    M[8]=2;
    N[9]=0;
    M[9]=0;
    addNulls(L,N,M);
    modeling(L,N,M,0);

    printf("end");

}
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