import java.util.Scanner;
//this program test input validation yes or no program
public class Fool
{
public static void main(String [] args)
{
String input;
char first;
Scanner keyboard=new Scanner(System.in);
System.out.println("Enter yes or no ");
input=keyboard.nextLine();
first=input.charAt(0);
System.out.print(first);
while( first !='y' || first !='n')
{
System.out.println("please enter yes or no");
}
}
}
What is trying to get the program to is that the user has to remain in the while loop if the user does not put in yes or no.
change this to
while( first !='y' || first !='n') {
System.out.println("please enter yes or no");
}
this
while( first !='y' && first !='n') {
System.out.println("please enter yes or no");
}
because (first !='y' || first !='n') is always true.
if first =='y' then first !='n' is true
if first =='n' then first !='y' is true.
so while condition is always true
what you need is not || but && [and ]
while( first !='y' || first !='n') is always true.
Replace your code with:
while( first !='y' && first !='n')
while( first !='y' || first !='n') is always true.
As OR operation works as follows
condition 1 condition 2 result
TRUE TRUE TRUE
TRUE FALSE TRUE
FALSE TRUE TRUE
FALSE FALSE FALSE
In your case one condition will be always true, therefore it enters in while loop everytime
While AND operation works as follows
condition 1 condition 2 result
TRUE TRUE TRUE
TRUE FALSE FALSE
FALSE TRUE FALSE
FALSE FALSE FALSE
so instead of using OR try using AND
e.g. while( first !='y' && first !='n')
You should change your code to
boolean b=false;
while(b==false){
if(first !='y' || first !='n'){
System.out.println("please enter yes or no");
} else {
b=true;
}
}
Related
Here is the code;
public class Main {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Do you need instructions for this game? Y/N.");
char a = input.next().charAt(0);
// This while loop always comes out as true.
while (a != 'y' || a != 'n') {
System.out.println("Please enter either Y/N. ");
System.exit(0);
}
if (a == 'y') {
System.out.println("This game is called heads and tails.");
System.out.println("You must type h (heads), or t (tails).");
System.out.println("You will need to keep guessing correctly, each correct guess will increase your score.");
}
}
}
Is there an explanation on why it always comes out as true, and is there an alternative way of doing this? I want to have a validation check, where if the user inputs anything other than y, or n, the program shuts down.
The problem is, when I enter the character, y, or n, it shuts down anyway even though I'm using the != (not equals) operator.
If you have a==y, then a != 'n' is true and a != 'y' || a != 'n' is true.
If you have a==n, then a != 'y' is true and a != 'y' || a != 'n' is true.
If you have a == other thing, a != 'y' || a != 'n' is true.
It is everytime true with the OR operation. Need use AND.
(a != 'y' || a != 'n') at least one of the sub-conditions must be true.
Consider the three possible cases:
a is 'y': false || true gives true
a is 'n': true || false gives true
a is something else: true || true gives true
The character a cannot both be y and n, so the while loop is executed for any input.
Besides, the loop is not looping.
You're checking whether a is not equal to 'y' OR a is not equal to 'n'.
This is always true.
Change it into while ((a != 'y') && (a != 'n')).
The condition inside while in
while (a != 'y' || a != 'n')
is always true because
if a is equal to y, then a is obviously not equal to n. So, result is true.
And again, if a is equal to n, then a is obviously not equal to y. So, result is true.
And again, if a is not equal to y or n, then also the result is true.
So, the condition inside the while is always true. And for this reason, the execution is entering the while loop and after printing your message it is exiting.
So using AND instead of OR may solve your problem, like
while(a != 'y' && a !='n') {
//your work
}
And I think you willing to do this like below,
public class Main {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Do you need instructions for this game? Y/N: ");
char a = input.next().charAt(0);
while (a != 'y') {
if(a =='n') {
System.exit(0);
}
else{
System.out.println("Please enter either Y/N : ");
a = input.next().charAt(0);
}
}
if (a == 'y') {
System.out.println("This game is called heads and tails.");
System.out.println("You must type h (heads), or t (tails).");
System.out.println("You will need to keep guessing correctly, each correct guess will increase your score.");
}
}
}
Your logic should be "a is not y and a is not n"
while (a != 'y' && a != 'n')
I'm trying to do a simple Hangman game for school.
In the beginning the user inputs a word as a String and the string is converted into a char Array, wordArray. Then a char Array starArray is created that has the same amount of elements as wordArray, and is filled with "*". Those start get replaced with letters as the letters are guessed correctly.
After this, I have this loop:
do {
System.out.println("Guess a letter:");
strGuess = scan.nextLine();
chGuess = strGuess.charAt(0);
//prompts the user to guess a letter and converts said letter to a char
for(int i = 0; i<Array.getLength(wordArray); i++){
if (chGuess == wordArray[i]){
starArray[i] = strGuess.charAt(0);
guessCorrect = true;
}
} //this happens if the guess is correct
if (guessCorrect == false){
System.out.println("Nope, wrong guess!");
wrongGuess = wrongGuess + 1;
System.out.println("You have " + (5-wrongGuess) + " lives left.");
} //if the guess isn't correct, amount of wrong guesses increases
guessCorrect = false; //the value of whether a guess is correct resets
for(int i=0;i<starArray.length;i++){
System.out.print(starArray[i]);
} //prints out the word with "*" in place of letters that haven't been guessed yet
/*if starArray == wordArray
wordGuessed = true;*/
} while (wrongGuess == 5 || wordGuessed == false); //if the word is guessed or the user has guessed wrong 5 times, the loop ends
Now this code isn't complete yet, so the "wordGuessed" part of the condition can never happen as of now - you can't win the game yet. However, the loop doesn't end when the wrongGuess value gets higher than 5. It will keep going, prompting the user to guess again and again. I checked and the wordGuessed value does in fact change correctly, do it does reach 5 after 5 wrong guesses.
If wordGuessed is always false, wordGuessed == false will always return true.
The condition to loop is that wrongGuess == 5 || wordGuessed == false is true.
Using the first statement, that could be replaced by: wrongGuess == 5 || true
That will also always be true as anything OR true is true.
You want to stop looping once (wrongGuess == 5 or wordGuessed == true).
In other words, loop while !((wrongGuess == 5) OR (wordGuessed == true)).
Basic boolean algebra, the reverse of A OR B is !A AND !B. You have to keep looping while wrongGuess != 5 && wordGuessed == false
Here's the code:
System.out.println("Qualifies for instate rate: ");
instate = keyboard.nextLine();
while((instate.equalsIgnoreCase("yes") == false || instate.equalsIgnoreCase("no") == false))
{
System.out.println("Enter either yes or no:");
instate = keyboard.nextLine();
}
My problem is the output is never-ending; here's the output
Enter either yes or no:
no
Enter either yes or no:
no
Enter either yes or no:
yes
Enter either yes or no:
yup
Enter either yes or no:
It doesn't even matter what I enter in the keyboard.
Please tell me the problem and possible solutions.
Change:
System.out.println("Qualifies for instate rate: ");
instate = keyboard.nextLine();
while((instate.equalsIgnoreCase("yes") == false || instate.equalsIgnoreCase("no") == false))
{
System.out.println("Enter either yes or no:");
instate = keyboard.nextLine();
}
To:
System.out.println("Qualifies for instate rate: ");
instate = keyboard.nextLine();
while((instate.equalsIgnoreCase("yes") == false && instate.equalsIgnoreCase("no") == false))
{
System.out.println("Enter either yes or no:");
instate = keyboard.nextLine();
}
Change your condition inside the while loop to be :
(instate.equalsIgnoreCase("yes") == false && instate.equalsIgnoreCase("no") == false)
It because of DeMorgan's Rule in Boolean Algebra:
!A || !B = !(A && B)
!A && !B = !(A || B)
Change your condition to the following:
!Arrays.asList(new String[]{"yes", "no"}).contains(instate.toLowerCase())
this line instate.equalsIgnoreCase("yes") already returns a boolean so you don't need to compare it again.. try this.
while((!instate.equalsIgnoreCase("yes")) && (!instate.equalsIgnoreCase("no")))
One of the boolean expression in the while condition will always be true. "instate" cannot be "yes" and "no" at the same time. If you like to terminate the loop on "no" input, try
while (!instate.equalsIgnoreCase("no")) {
}
In your while loop condition:
while((instate.equalsIgnoreCase("yes") == false || instate.equalsIgnoreCase("no") == false))
{
System.out.println("Enter either yes or no:");
instate = keyboard.nextLine();
}
You have it testing if either "yes" is not the input or "no" is not the input, so if they type "yes", it will see that they didn't type "no", then repeat the loop, and if they typed "no", it will see that yes was not typed and repeat again. Change the || operator to the && operator so it makes sure that if either "yes" or "no" is typed, and if neither is typed, then it will repeat.
while((instate.equalsIgnoreCase("yes") == false && instate.equalsIgnoreCase("no") == false))
{
System.out.println("Enter either yes or no:");
instate = keyboard.nextLine();
}
I tried using a loop to get a proper desired input from the user. The loop just doesn't stop. I brainstormed for a while but could not patch the bug.
char choice;
System.out.println("Below is a auto generated description for your property.Is it okay for you? (y/n)");
choice = sc.next().charAt(0);
for(;(choice!='y' || choice !='Y' || choice!='n' || choice !='N' );)
{
choice = sc.next().charAt(0);
System.out.println("Please enter 'y' or 'n'.");
}
// ... other codes ... //
Please help!
Thank you.
choice != 'y' || choice != 'Y'
The above test will always be true. If choice is y, then choice != 'Y' is true, and the whole condition is thus also true. If choice is Y, then choice != 'y' is true, and the whole condition is thus also true.
You want && instead of ||.
Also, for (; condition;) is more readable when written as while (condition).
for(; !(choice=='y' || choice =='Y' || choice=='n' || choice =='N' ) ;)
{
choice = sc.next().charAt(0);
System.out.println("Please enter 'y' or 'n'.");
}
Just add a !. In my opinion, while loop is more suitable here.
while(user did not enter y or n){
// loop
}
Use below code
you should use && operator inside for or while loop.
Scanner sc = new Scanner(System.in);
char choice;
System.out.println("Below is a auto generated description for your property.Is it okay for you? (y/n)");
choice = sc.next().charAt(0);
while(choice!='y' && choice !='Y' && choice!='n' && choice !='N' ){
System.out.println("Please enter 'y' or 'n'.");
choice = sc.next().charAt(0);
}
I want to exit the while loop when the user enters 'N' or 'n'. But it does not work. It works well with one condition but not two.
import java.util.Scanner;
class Realtor {
public static void main (String args[]){
Scanner sc = new Scanner(System.in);
char myChar = 'i';
while(myChar != 'n' || myChar != 'N'){
System.out.println("Do you want see houses today?");
String input = sc.next();
myChar = input.charAt(0);
System.out.println("You entered "+myChar);
}
}
}
You need to change || to && so that both conditions must be true to enter the loop.
while(myChar != 'n' && myChar != 'N')
Your condition is wrong. myChar != 'n' || myChar != 'N' will always be true.
Use myChar != 'n' && myChar != 'N' instead
If your code, if the user enters 'X' (for instance), when you reach the while condition evaluation it will determine that 'X' is differente from 'n' (nChar != 'n') which will make your loop condition true and execute the code inside of your loop. The second condition is not even evaluated.