A Simple Cross-platform Program

void solutionconstruct();  //setup start array
void setnumber(int x, int y, int number);  //number selected in the sudoku
void generatesudoku(int start);  //generate a sudoku from "start"
void checkselection(void);  //see if one or two numbers can be selected
int findsingle(void);  //select standalone number and return if found
void getgame(int level);   //select hard,medium or easy random game
void solvehere();  //solve existing sudoku

//constructor to setup sudokuarray
void solutionconstruct()
{
//fill the "0" step with pencil 1-9 in all the small squares -81 of them
char number =1;
int xl = 0;
for(xl;xl<=2;xl++)
{
 int yl = 0;
 for(yl;yl<=2;yl++)
 {
  int xs = 0;
  for(xs;xs<=2;xs++)
  {
   int ys = 0;
   for(ys;ys<=2;ys++)
   {
    int yn = 0;
    for(yn;yn<=2;yn++)
	{ 
     int xn = 0;
     for(xn;xn<=2;xn++)
	 {
      sudokuarray[0][xl][yl][xs][ys][xn][yn] = number;//fill the first step
      number = number + 1;  //put in 1 to 9
	 }//next xn
	}//next yn
      number=1;  //1 to 9 in box now do next
   }//next ys
  }//next xs
 }//next yl
}//next xl...............................all done
}//end of constructor

void setnumber(int x, int y, int number)
{//values 0 t0 8
	if(sudokustep < 81)  // cant go on if last number selected
    {
int selected = 0;  //check to see if number already selected
int nopossible = 0;  //check to see if no possibilities to select exist
int crossedout = 0;  //check to see if the number has been crossed out
if(sudokuarray[sudokustep][x/3][y/3][x%3][y%3][number%3][number/3] == 0)
crossedout = 1;  //the number has been crossed out
   int yn = 0;
   for(yn;yn<=2;yn++)  // in this number box
	{ 
     int xn = 0;
     for(xn;xn<=2;xn++)
	 {      
      if (sudokuarray[sudokustep][x/3][y/3][x%3][y%3][xn][yn] > 9) 
		  selected = 1; //this number already selected
      if (sudokuarray[sudokustep][x/3][y/3][x%3][y%3][xn][yn] > 0)
		  nopossible = 1;  //at least one possible number exists
	 }//next xn
	}//next yn
   if((selected < 1) && (nopossible > 0) && (crossedout < 1))  //number not selected 
   {//could move on to next step if a its a possible and its not crossed out
int xl = 0;
for(xl;xl<=2;xl++)    //copy the current step values 
{
 int yl = 0;
 for(yl;yl<=2;yl++)   //to the next step
 {
  int xs = 0;
  for(xs;xs<=2;xs++)
  {
   int ys = 0;
   for(ys;ys<=2;ys++)
   {
    int yn = 0;
    for(yn;yn<=2;yn++)
	{ 
     int xn = 0;  
     for(xn;xn<=2;xn++)
	 {
      sudokuarray[sudokustep + 1][xl][yl][xs][ys][xn][yn] = 
      sudokuarray[sudokustep][xl][yl][xs][ys][xn][yn]; //array copy
	 }//next xn
	}//next yn
   }//next ys
  }//next xs
 }//next yl
}//next xl...............................all done
sudokustep = sudokustep +1; //work on the next step update the number box
char savenumber=sudokuarray[sudokustep][x/3][y/3][x%3][y%3][number%3][number/3] + 10;
int j = 0;
for (j; j <= 2; j++)  //set all to zero except selected number in box
{
 int i = 0;
 for ( i; i <= 2; i++)
 {
	 if(sudokuarray[sudokustep][x/3][y/3][x%3][y%3][i][j] <10)
   sudokuarray[sudokustep][x/3][y/3][x%3][y%3][i][j] = 0;
 }//end of i for
}// end of j for
j = 0;
for (j; j <= 2; j++)  //horizontal line cannot have this number
{
 int i = 0;
 for (i;  i <= 2; i++)
 {
	 if(sudokuarray[sudokustep][j][y/3][i][y%3][number%3][number/3] < 10)
   sudokuarray[sudokustep][j][y/3][i][y%3][number%3][number/3] = 0;
 }//end of i for
}// end of j for
j = 0; 
for (j; j <= 2; j++)  //vertical line cannot have this number
{
 int i = 0;
 for ( i; i <= 2; i++)
 {
	 if(sudokuarray[sudokustep][x/3][j][x%3][i][number%3][number/3] < 10)
   sudokuarray[sudokustep][x/3][j][x%3][i][number%3][number/3] = 0;
 }//end of i for
}// end of j for
j = 0;
for (j; j <= 2; j++)  //box of 9 numbers cannot have this number
{
 int i = 0;
 for ( i; i <= 2; i++)
 {
	 if(sudokuarray[sudokustep][x/3][y/3][j][i][number%3][number/3] < 10)
   sudokuarray[sudokustep][x/3][y/3][j][i][number%3][number/3] = 0;
 }//end of i for
}// end of j for

//restore the selected number
sudokuarray[sudokustep][x/3][y/3][x%3][y%3][number%3][number/3]=savenumber;
}//end of number not already selected & possible & not crossed out selected if
}// end of less than 81 step if
}// end of set number function

void generatesudoku(int start)  //generate a sudoku from "start"
{
sudokustep = start; //start the sudoku solution
int blank = 0;  //if get blank cant solve
while((blank == 0) && (sudokustep < 80))  //check for blank
{
int x = rand() % 9;   //get random x value
int y = rand() % 9;   //get random y value
int number = rand() % 9;   //get random number value
setnumber(x,y,number);  //select if can in solution
checkselection();   //select any stanalone numbers
int xl = 0;
for(xl;xl<=2;xl++)
{
 int yl = 0;
 for(yl;yl<=2;yl++)
 {
  int xs = 0;
  for(xs;xs<=2;xs++)
  {
   int ys = 0;
   for(ys;ys<=2;ys++)
   {
    int numberselected = 0;  //find how many zero's in this box
    int yn = 0;
    for(yn;yn<=2;yn++)
	{ 
     int xn = 0;
     for(xn;xn<=2;xn++)
	 {
     if( sudokuarray[sudokustep][xl][yl][xs][ys][xn][yn] == 0)
       numberselected += 1;  //count number in this box
	 }//next xn
	}//next yn
	 if(numberselected == 9)
		 blank=1;
   }//next ys
  }//next xs
 }//next yl
}//next xl...............................all done
}//end of check for blank
}//end of generate a sudoku

void checkselection(void)  //see if one or two numbers can be selected
{
if(findsingle() == 0)  //find if one can be selected
findsingle();
}// end of check selection

int findsingle(void)  //select standalone number and return if found
{
int bignumber = 0;  //holds the selected number
int nonselect = 1;  //flag for standalone number = 0 for true
int xl = 0;
for(xl;xl<=2;xl++)
{
 int yl = 0;
 for(yl;yl<=2;yl++)
 {
  int xs = 0;
  for(xs;xs<=2;xs++)
  {
   int ys = 0;
   for(ys;ys<=2;ys++)
   {
    int numberselected = 0;  //find how many zero's in this box
    int yn = 0;
    for(yn;yn<=2;yn++)
	{ 
     int xn = 0;
     for(xn;xn<=2;xn++)
	 {
     if( sudokuarray[sudokustep][xl][yl][xs][ys][xn][yn] == 0)
       numberselected += 1;  //count number in this box
	 else
		 bignumber = sudokuarray[sudokustep][xl][yl][xs][ys][xn][yn];
	 }//next xn
	}//next yn
	 if((numberselected == 8) && (bignumber < 10))
	 {
	 setnumber(xl *3 + xs,yl *3 + ys,bignumber -1);  //select the stadalone
     nonselect = 0;  //we have found a stad alone number
	 }//end of number selected if
   }//next ys
  }//next xs
 }//next yl
}//next xl...............................all done
return nonselect;  
}//end of select standalone number

void getgame(int level)   //select hard,medium or easy random game
{
sudokustep = 0;  //start
while(sudokustep <81 )  //try until have complete solution
{
generatesudoku(0);
}//end of complete solution
sudokustep = level;  //hard, medium or easy sudoku
}//end of get game

void solvehere()  //solve existing sudoku
{
int start = sudokustep;  //starting position
int count = 0;  //if goes on to long cant solve
while(sudokustep <81 )  //try until have complete solution
{
generatesudoku(start);
count = count + 1;
if(count > 500)
break;   //gone on to long cant solve
findsingle();  //have to do last here
}//end of complete solution
}//end of solve existing sudoku