very simple brute force sudoku solve program in C

     In my college first year, I heard Sivakumar telling about his friend's brother who created a c program to solve sudoku. At that time I was thinking it was very hard and that guy who created that program is very intelligent. Because I never solved even a single sudoku puzzle. Sometimes I sat for hours and it will go wrong in at last.

     Till yesterday I never thought that I am able write a program to solve a sudoku puzzle. But this bike accident made me to sit alone in room and I had nothing to do. Siva came into mind as well as the puzzle program. I just gave a thought. Viola the concept is very simple. Brute-force! the all time success methodology will solve this puzz in minutes even in worst case.

    Here I have attached my code which is less than 200 lines.

    Also read the code here. And please update me if it is having any issues.

sudoku.h
#ifndef SUDOKU_H
#define SUDOKU_H 1
#define ZERO 0
#define MAX 9
#define PASS 0
#define FAIL 1
#define FIXED 0
#define WORKING 1
#define TOWORK 2
typedef struct element {
    int val;
    int status;
} element;
extern element elm[MAX][MAX];
void get_input();
int next_elm();
int check(int, int);
void show();
#endif

main.c
#include <stdio.h>
#include "sudoku.h"
element elm[MAX][MAX];
int main() {
    printf("SUDOKU PROGRAM BY theB\n");
    get_input();
    int ret = next_elm();
    if (ret == PASS) {
        show();
    }
    else {
        printf("INPUT ERROR\n");
    }
    return 0;
}

get_input.c
#include <stdio.h>
#include "sudoku.h"
void get_input() {
    int i, j;
    for (i = 0; i < MAX ; i++) {
        for (j = 0; j < MAX; j++) {
            printf("ENTER elm[%d][%d]: ", i, j);
            scanf("%d", &elm[i][j].val);

            if (elm[i][j].val)
                elm[i][j].status = FIXED;
            else
                elm[i][j].status = TOWORK;
        }
    }
}

check.c
#include <stdio.h>
#include "sudoku.h"
int check(int x, int y) {
    int i, j;
    //CHECK HORIZONTAL
    for (i = 0; i < MAX; i++) {
        if ((elm[x][y].val == elm[i][y].val) && (x != i))
            return FAIL;
    }
    //CHECK VERTICAL
    for (i = 0; i < MAX; i++) {
        if ((elm[x][y].val == elm[x][i].val) && (y != i))
            return FAIL;
    }
    //CHECK BOXES
    int startx = (x / 3) * 3;
    int starty = (y / 3) * 3;
    for (i = startx; i < startx + 3; i++) {
        for (j = starty; j < starty + 3; j++) {
            if ((elm[x][y].val == elm[i][j].val) && (x != i) && (y != j)) {
                return FAIL;
            }
        }
    }
    return PASS;
}

next_elm.c
#include <stdio.h>
#include "sudoku.h"
int next_elm() {
    int i, j, k;
    for (i = 0; i < MAX; i++) {
        for (j = 0; j < MAX; j++) {
            if (elm[i][j].status == TOWORK)
                goto L;
        }
    }
    return PASS;
    L:
    for (k = 1; k <= MAX; k++) {
        elm[i][j].val = k;
        elm[i][j].status = WORKING;
        int ret = check(i, j);
        if (ret == FAIL)
            continue;
        else if (ret == PASS) {
            ret = next_elm();
            if (ret == PASS)
                return PASS;
            else
                continue;
        }
    }
    elm[i][j].val = 0;
    elm[i][j].status = TOWORK;
    return FAIL;
}