Code-cracking%20skills%20can%20be%20put%20to%20the%20test%20in%20this%20entertaining%20book%20which%20teaches%20children%20how%20to%20write%20and%20decode%20secret%20messages.%20Includes%20Semaphore%20and%20Morse%20code%2C%20the%20Grid%20code%20used%20in%20the%20American%20Civil%20War%2C%20Egyptian%20hieroglyphics%2C%20number%20replacement%20and%20alphabet%20switching%20codes%20and%20more.%20Each%20page%20features%20a%20different%20type%20of%20code%2C%20with%20an%20explanation%20of%20how%20it%20works%20and%20a%20practice%20code%20to%20crack.%20All%20answers%20are%20available%20at%20the%20back%20of%20the%20book.