The importance of data security allows us to restrict the user from providing invalid input. In order to avoid a problem or a “bug” in the software, you must restrict the user’s input with some interval of possible values

Example: Write a program that asks the user to enter a value between 0-5. If the user provides you with invalid input, your program shall run again until the user satisfies the request. 

·   Selection of loop: Do-while, since we will ask for the user’s input first

·   What is the condition:

• While input < 0 || input > 5

• While input >= 0  && input <= 5       

You have three options to validate user input: 

Option #1 Validating by flipping the logic (post-test)

int x;

do{

System.out.println("Enter a number [0,5]");

x = input.nextInt();

}while(x < 0 || x > 5);

System.out.println("Thank you");

Option #2: Sentinel or Flags

int n;

boolean sentinel = true;

while(sentinel)

{

System.out.println("Please enter a value between 0 and 5");

n = input.nextInt();

if(n >= 0 && n <= 5)

sentinel = false;

}

System.out.println("Thank you for entering the correct value");

Option #3: Making an infinite loop and use the break “emergency exit”

while(true)

{

System.out.println("Please enter a value between 0 and 5");

int n = input.nextInt();

if(n >= 0 && n <= 5){

break;

  }

}

System.out.println("Thank you for entering the correct value");