Write clearScreen function

src/main/c/VierGewinnt.c

@@ -125,4 +125,11 @@ void printBoard(char board[ROWS][COLS]) {
 
     printf("  1   2   3   4   5   6   7\n\n");
 }
-
+// Write clearScreen function
+void clearScreen() {
+#ifdef _WIN32
+    system("cls");
+#else
+    system("clear");
+#endif
+}