I need a Sudoku game solver in C programming (Not C++). Standard 9 by 9. It need

Question

I need a Sudoku game solver in C programming (Not C++). Standard 9 by 9. It needs to request the user for the setup (known and unknowns) using 0s, or spaces or dots for the unknowns. After all 9x9 constants and variables have been input by the user, it will print the 9 by 9 result (in a nice squared drawn box if possible). Super thank u very much in advance for you kind help.

It will look something like this.

Please enter layout using "0" for unknowns/variables:

100060002

000400000

000000006

000000200

000300006

000100200

020008000

000030000

005001000

One possible solution is:

9 4 6 9 4 3 6 3 5

7 3 6 9 4 8 5 2 5

6 2 6 7 8 9 3 2 6

4 9 7 6 5 1 3 5 9

1 3 7 4 2 6 9 1 4

4 3 4 6 9 4 3 1 6

6 4 1 2 9 6 4 2 8

6 3 2 7 6 4 6 3 5

7 5 4 1 9 7 5 3 5

Explanation / Answer

#include <stdio.h>

int isAvailable(int puzzle[][9], int row, int col, int num)
{
    int rowStart = (row/3) * 3;
    int colStart = (col/3) * 3;
    int i, j;

    for(i=0; i<9; ++i)
    {
        if (puzzle[row][i] == num) return 0;
        if (puzzle[i][col] == num) return 0;
        if (puzzle[rowStart + (i%3)][colStart + (i/3)] == num) return 0;
    }
    return 1;
}

int fillSudoku(int puzzle[][9], int row, int col)
{
    int i;
    if(row<9 && col<9)
    {
        if(puzzle[row][col] != 0)
        {
            if((col+1)<9) return fillSudoku(puzzle, row, col+1);
            else if((row+1)<9) return fillSudoku(puzzle, row+1, 0);
            else return 1;
        }
        else
        {
            for(i=0; i<9; ++i)
            {
                if(isAvailable(puzzle, row, col, i+1))
                {
                    puzzle[row][col] = i+1;
                    if((col+1)<9)
                    {
                        if(fillSudoku(puzzle, row, col +1)) return 1;
                        else puzzle[row][col] = 0;
                    }
                    else if((row+1)<9)
                    {
                        if(fillSudoku(puzzle, row+1, 0)) return 1;
                        else puzzle[row][col] = 0;
                    }
                    else return 1;
                }
            }
        }
        return 0;
    }
    else return 1;
}

int main()
{
    int i, j;
    int puzzle[9][9]={{0, 0, 0, 3, 0, 0, 0, 9, 0},
                      {1, 9, 0, 4, 7, 0, 6, 0, 8},
                      {0, 5, 2, 8, 1, 9, 4, 0, 7},
                      {2, 0, 0, 0, 4, 8, 0, 0, 0},
                      {0, 0, 9, 0, 0, 0, 5, 0, 0},
                      {0, 0, 0, 7, 5, 0, 0, 0, 9},
                      {9, 0, 7, 3, 6, 4, 1, 8, 0},
                      {5, 0, 6, 0, 8, 1, 0, 7, 4},
                      {0, 8, 0, 0, 0, 0, 0, 0, 0}};

    if(fillSudoku(puzzle, 0, 0))
    {
        printf(" +-----+-----+-----+ ");
        for(i=1; i<10; ++i)
        {
            for(j=1; j<10; ++j) printf("|%d", puzzle[i-1][j-1]);
            printf("| ");
            if (i%3 == 0) printf("+-----+-----+-----+ ");
        }
    }
    else printf(" NO SOLUTION ");

    return 0;
}

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