diff --git a/forth.c b/forth.c
new file mode 100644
index 0000000..09e6cbc
--- /dev/null
+++ b/forth.c
@@ -0,0 +1,128 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+#define SIZE 9
+
+void printSudoku(int board[SIZE][SIZE]) {
+    for (int i = 0; i < SIZE; i++) {
+        for (int j = 0; j < SIZE; j++) {
+            if (j % 3 == 0 && j != 0) {
+                printf("| ");
+            }
+            printf("%d ", board[i][j] == 0 ? '.' : board[i][j]);
+        }
+        printf("\n");
+        if ((i + 1) % 3 == 0 && i != 8) {
+            printf("---------------------\n");
+        }
+    }
+}
+
+bool isValidPlacement(int board[SIZE][SIZE], int row_check[SIZE][SIZE], int col_check[SIZE][SIZE],
+    int block_check[SIZE][SIZE], int num, int row, int col) {
+    int blockIndex = (row / 3) * 3 + (col / 3);
+    if (row_check[row][num - 1] || col_check[col][num - 1] || block_check[blockIndex][num - 1]) {
+        return false; // 数字已在行、列或3x3块中存在
+    }
+    return true;
+}
+
+void setPlacement(int row_check[SIZE][SIZE], int col_check[SIZE][SIZE],
+    int block_check[SIZE][SIZE], int num, int row, int col, bool placed) {
+    int blockIndex = (row / 3) * 3 + (col / 3);
+    row_check[row][num - 1] = placed;
+    col_check[col][num - 1] = placed;
+    block_check[blockIndex][num - 1] = placed;
+}
+
+bool isValidSudoku(int board[SIZE][SIZE]) {
+    int row_check[SIZE][SIZE] = { 0 };
+    int col_check[SIZE][SIZE] = { 0 };
+    int block_check[SIZE][SIZE] = { 0 };
+
+    for (int i = 0; i < SIZE; i++) {
+        for (int j = 0; j < SIZE; j++) {
+            int num = board[i][j];
+            if (num != 0) {
+                if (!isValidPlacement(board, row_check, col_check, block_check, num, i, j)) {
+                    printf("False: Invalid initial Sudoku matrix!\n");
+                    printf("The number %d has conflicts!\n", num);
+                    return false;
+                }
+                setPlacement(row_check, col_check, block_check, num, i, j, true);
+            }
+        }
+    }
+    return true;
+}
+
+bool solveSudoku(int board[SIZE][SIZE]) {
+    for (int i = 0; i < SIZE; i++) {
+        for (int j = 0; j < SIZE; j++) {
+            if (board[i][j] == 0) { // 找到一个空的位置
+                for (int num = 1; num <= 9; num++) {
+                    board[i][j] = num; // 填入数字
+
+                    if (isValidSudoku(board)) {
+                        if (solveSudoku(board)) {
+                            return true; // 若成功，则返回
+                        }
+                    }
+                    board[i][j] = 0; // 撤销填入，重试下一个数字
+                }
+                return false; // 若所有数字尝试均不行，则返回不成功
+            }
+        }
+    }
+    return true; // 全部填满，返回成功
+}
+
+int main() {
+    int board0[SIZE][SIZE] = {
+        {5, 3, 0, 0, 7, 0, 0, 0, 0},
+        {6, 0, 0, 1, 9, 5, 0, 0, 0},
+        {0, 9, 8, 0, 0, 0, 0, 6, 0},
+        {8, 0, 0, 0, 6, 0, 0, 0, 3},
+        {4, 0, 0, 8, 0, 3, 0, 0, 1},
+        {7, 0, 0, 0, 2, 0, 0, 0, 6},
+        {0, 6, 0, 0, 0, 0, 2, 8, 0},
+        {0, 0, 0, 4, 1, 9, 0, 0, 5},
+        {0, 0, 0, 0, 8, 0, 0, 7, 9}
+    };
+
+    int board1[SIZE][SIZE] = {
+        {8, 3, 0, 0, 7, 0, 0, 0, 0},
+        {6, 0, 0, 1, 9, 5, 0, 0, 0},
+        {0, 9, 8, 0, 0, 0, 0, 6, 0},
+        {8, 0, 0, 0, 6, 0, 0, 0, 3},
+        {4, 0, 0, 8, 0, 3, 0, 0, 1},
+        {7, 0, 0, 0, 2, 0, 0, 0, 6},
+        {0, 6, 0, 0, 0, 0, 2, 8, 0},
+        {0, 0, 0, 4, 1, 9, 0, 0, 5},
+        {0, 0, 0, 0, 8, 0, 0, 7, 9}
+    };
+
+    for (int boardIndex = 0; boardIndex < 2; boardIndex++) {
+        int (*currentBoard)[SIZE] = boardIndex == 0 ? board0 : board1;
+
+        printf("The original Sudoku matrix:\n");
+        printSudoku(currentBoard);
+        if (isValidSudoku(currentBoard)) {
+            printf("True: Valid initial Sudoku matrix!\n");
+            if (solveSudoku(currentBoard)) {
+                printf("The solution of Sudoku matrix:\n");
+                printSudoku(currentBoard);
+            }
+            else {
+                printf("No solution!\n");
+            }
+        }
+        else {
+            printf("False: Invalid initial Sudoku matrix!\n");
+            printf("No solution!\n");
+        }
+        printf("\n");
+    }
+
+    return 0;
+}