> ./game.out sample_equation2.txt --challenge_mode
Let's play a guessing game!
The secret is an equation with 6 characters.
your guess: 11-8=3

+-----------------------------------+
|.....                   .....      |
|.   .                   .   .      |
|. 1 .   1     -     8   . = .   3  |
|.   .                   .   .      |
|.....                   .....      |
+-----------------------------------+

your guess: 7*3=21
ERROR: character '3' appears at most 0 time(s)
your guess: 6*4=24
ERROR: character '1' appears at least 1 time(s)
your guess: 7*2=14

+-----------------------------------+
|                  ***** ***** *****|
|                  *   * *   * *   *|
|  7     *     2   * = * * 1 * * 4 *|
|                  *   * *   * *   *|
|                  ***** ***** *****|
+-----------------------------------+

your guess: 4+9=13
ERROR: character [5] of the guess should be '4'
ERROR: character [5] of the guess cannot be '3'
ERROR: character '3' appears at most 0 time(s)
your guess: 5+9=14

+-----------------------------------+
|..... ***** ..... ***** ***** *****|
|.   . *   * .   . *   * *   * *   *|
|. 5 . * + * . 9 . * = * * 1 * * 4 *|
|.   . *   * .   . *   * *   * *   *|
|..... ***** ..... ***** ***** *****|
+-----------------------------------+

your guess: 9+5=14

+-----------------------------------+
|***** ***** ***** ***** ***** *****|
|*   * *   * *   * *   * *   * *   *|
|* 9 * * + * * 5 * * = * * 1 * * 4 *|
|*   * *   * *   * *   * *   * *   *|
|***** ***** ***** ***** ***** *****|
+-----------------------------------+

CONGRATULATIONS!
You solved the puzzle after making 4 guesses!