Implement switch/case or if/else ladder for menu control. Update the currency conversion program. If the user enters an invalid input the program should loop back and allow the user to re-enter input until user input is valid or have a count for how many times the user can input values. If user input in the menu is invalid allow the user to re-enter input until user input is valid or have a count for how many times the user can input values.

the major difference between the two is the objective and the reward of the game. candy crush has a puzzle theme with the objective of meeting a specific quota of points or objects, you are able to gain access to the next level and compete with peers on the process. on duolingo the objective is rather different, you are given sets of questions for you to answer for you to move to the next level and as for the reward, you are able to learn available language as this is an app developed to teach the user about other languages.