Answer:
EventHandler
Explanation:
In order to do this the programmer needs to use the EventHandler class. This class allows the computer to listen for certain user actions such as pressing a button. Using this on a button would then allow the programmer to specify what they want to happen when the user clicks the button or performs a certain action. For example, in this scenario, the programmer would program an EventHandler so that when the button is clicked it saves the input to a variable and changes the input field to the next option.
B) For Military Purposes but around the 1970s they became widely available to consumers.
Text boxes and related tools
Your question wasn't very clear, but I think I understand what you want. Additionally, you should really state what language you're working with. Here it is in C#, and shouldn't be too much of a hassle to translate in to other languages.
Console.Write("Enter payment: ");
float payment;
if (float.TryParse(Console.ReadLine(), out payment))
Console.WriteLine((Math.Floor(payment * 100) / 100) * 0.15, + " at 15% tip.");
else
Console.WriteLine("Invalid input.");
