How to use a (while) loop and where to place it if eligible for all code

Here is some pseudocode to illustrate:

while true get input if input is -999 (or other conditions) break out of loop else // rest of code goes here 

So basically, wrap the whole thing in a while true loop and then use the conditional logic to break out of the loop when certain conditions are met.

On c++, im trying to make a program that will repeatedly accept the input of the user unless - 999 is pressed. Additionally, if the input is not divisible by 5 or 20, then I asked for it to output "must enter divisible by 5 or 20."

#include <limits> // std::numeric_limits<> #include <iostream> int main() { for (;;) { // forever int value; while (std::cout << "Thou must enter a value divisible by 5 or 20. When finished enter -999 to leave.\n", !(std::cin >> value) || value != -999 && value % 5 != 0 && value % 20 != 0) // ^^ extraction failed or value does not conform to requirements { std::cerr << "Input error :(\nYou must enter a number divisible by 5 or 20.\n"; std::cin.clear(); // clear the flags that might have been set by a // failed input operation. std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // ^^ discards up to the maximum value of std::streamsize characters // until a newline character ('\n') is encountered. If we don't do that // the next input operation will choke on the same erroneous input. } if (value == -999) break; // do sth with value } } 

I want this to continue being done until they enter -999 but I do not know where to put my while loop or what to put if it is not entered. I also do not know where to put the "when finished enter -999 to leave" while making it eligible for all times and not just the start.

Perhaps you might want to break the problem down. Firstly, you would know that the "end condition" of this loop would be that the user keyed in -999. Hence you would want your loop to look something like

while userinput != -999 // do something here end while loop 

With that, all we need is to place the capturing of user input. One would be at the start, and one just before the while loop ends.

get userinput while userinput != -999 // do something here get userinput end while loop 

There are several ways to approach this problem, and that's depending on how you want to design your code. Here's my approach for this:

#include <iostream> void Request(int& amount) { std::cout << "Please enter the amount of money you would like to dispense (must be in 20's or 5's)" << std::endl; std::cout << "when finished, enter -999 to leave" << std::endl; std::cout << ">"; std::cin >> amount; } int main(void) { int amount = 0; for (Request(amount); amount != -999; Request(amount)) { // Since 20 is a multiple of 5, just check if its divisble by 5 will do if (amount % 5) { std::cout << "You must enter multiples of twenty or five only!" << std::endl; continue; } // Otherwise print out (or do stuff here) std::cout << amount % 5 << std::endl; } std::cout << "Thank you for doing business." << std::endl; }