Sudoku solver

//Sudoku solver created by Singapore's Prime Minister Lee Hsien Loong
//I did some small changes so it compiles with pedantic settings and Wextra, Wall, Werror

#include "stdio.h"


int InBlock[81], InRow[81], InCol[81];

const int BLANK = 0;
const int ONES = 0x3fe;     // Binary 1111111110

int Entry[81];  // Records entries 1-9 in the grid, as the corresponding bit set to 1
int Block[9], Row[9], Col[9];   // Each int is a 9-bit array

int SeqPtr = 0;
int Sequence[81];

int Count = 0;
int LevelCount[81];


void SwapSeqEntries(int S1, int S2)
{
     int temp = Sequence[S2];
     Sequence[S2] = Sequence[S1];
     Sequence[S1] = temp;
}


void InitEntry(int i, int j, int val)
{
     int Square = 9 * i + j;
     int valbit = 1 << val;
     int SeqPtr2;

     // add suitable checks for data consistency

     Entry[Square] = valbit;
     Block[InBlock[Square]] &= ~valbit;
     Col[InCol[Square]] &= ~valbit; // Simpler Col[j] &= ~valbit;
     Row[InRow[Square]] &= ~valbit; // Simpler Row[i] &= ~valbit;

     SeqPtr2 = SeqPtr;
     while (SeqPtr2 < 81 && Sequence[SeqPtr2] != Square)
           SeqPtr2++ ;

     SwapSeqEntries(SeqPtr, SeqPtr2);
     SeqPtr++;
}


void PrintArray()
{
     int i, j, valbit, val, Square;
     char ch = 0;

     Square = 0;

     for (i = 0; i < 9; i++) {
         if (i % 3 == 0) putc('\n', stdout);
         for (j = 0; j < 9; j++) {
             if (j % 3 == 0) putc(' ', stdout);
             valbit = Entry[Square++];
             if (valbit == 0) ch = '-';
             else {
                 for (val = 1; val <= 9; val++)
                     if (valbit == (1 << val)) {
                        ch = '0' + val;
                        break;
                     }
             }
             putc(ch,stdout);
         }
         putc ('\n', stdout);
     }
}


void ConsoleInput()
{
     int i, j;
     char InputString[80];

     for (i = 0; i < 9; i++) {
         printf("Row[%d] : ", i + 1);
         scanf("%s", InputString);

         for (j = 0; j < 9; j++) {
             char ch = InputString[j];
             if (ch >= '1' && ch <= '9')
                InitEntry(i, j, ch - '0');
         }
     }

     PrintArray();
}


void PrintStats()
{
    int i, S;

    printf("\nLevel Counts:\n\n");

    S = 0;
    while (LevelCount[S] == 0) S++;

    i = 0;

    while (S < 81) {
          int Seq = Sequence[S];
          printf("(%d, %d):%4d ", Seq / 9 + 1, Seq % 9 + 1, LevelCount[S]);
          if (i++ > 4){
             printf("\n");
             i = 0;
          }
          S++;
    }

    printf("\n\nCount = %d\n", Count);
}


void Succeed()
{
     PrintArray();
     PrintStats();
}


int NextSeq(int S)
{
    int S2 = 0, Square, Possibles, BitCount;
    int T, MinBitCount = 100;

    for (T = S; T < 81; T++) {
        Square = Sequence[T];
        Possibles = Block[InBlock[Square]] & Row[InRow[Square]] & Col[InCol[Square]];
        BitCount = 0;
        while (Possibles) {
           Possibles &= ~(Possibles & -Possibles);
           BitCount++;
        }

        if (BitCount < MinBitCount) {
           MinBitCount = BitCount;
           S2 = T;
        }
    }

    return S2;
}


void Place(int S)
{
    LevelCount[S]++;
    Count++;

    if (S >= 81) {
       Succeed();
       return;
    }

    int S2 = NextSeq(S);
    SwapSeqEntries(S, S2);

    int Square = Sequence[S];

    int     BlockIndex = InBlock[Square],
            RowIndex = InRow[Square],
            ColIndex = InCol[Square];

    int     Possibles = Block[BlockIndex] & Row[RowIndex] & Col[ColIndex];
    while (Possibles) {
          int valbit = Possibles & (-Possibles); // Lowest 1 bit in Possibles
          Possibles &= ~valbit;
          Entry[Square] = valbit;
          Block[BlockIndex] &= ~valbit;
          Row[RowIndex] &= ~valbit;
          Col[ColIndex] &= ~valbit;

          Place(S + 1);

          Entry[Square] = BLANK; // Could be moved out of the loop
          Block[BlockIndex] |= valbit;
          Row[RowIndex] |= valbit;
          Col[ColIndex] |= valbit;
    }

    SwapSeqEntries(S, S2);
}


int main()
{
    int i, j, Square;

    for (i = 0; i < 9; i++)
        for (j = 0; j < 9; j++) {
            Square = 9 * i + j;
            InRow[Square] = i;
            InCol[Square] = j;
            InBlock[Square] = (i / 3) * 3 + ( j / 3);
        }


    for (Square = 0; Square < 81; Square++) {
        Sequence[Square] = Square;
        Entry[Square] = BLANK;
        LevelCount[Square] = 0;
    }

    for (i = 0; i < 9; i++)
        Block[i] = Row[i] = Col[i] = ONES;

    ConsoleInput();
    Place(SeqPtr);
    printf("\n\nTotal Count = %d\n", Count);

    return 0;
}