Reputation: 47

What is wrong with my JAVA do loop?

I am learning JAVA and trying to write my first loop. The loop should prompt the user to guess a defined name.

The code is not performing right. I have tried to search for help on different JAVA tuturials both not found any examples where you guess a name/string but a lot where you should guess a number.

This is my code:

 /**
     *
     * @author mso_
     */
    import java.util.Scanner;

    public class GuessName {

        /**
         * @param args the command line arguments
         */

        public static final int C_Max_Trials = 10;

        public static void main(String[] args) {
            //Define correct name
            String name = "Morten";
            String guessName;

            //Create a scanner
            Scanner guess = new Scanner(System.in);

            //Recieve a guess
            do {
            System.out.println("Please guess my name. Enter your guess here: ");
            String guessName = guess.next(); <-- ERROR

            //Create loop
            } while (guessName != name); <-- ERROR
                System.out.println("Sorry, wrong guess, please enter another guess: ");

              if (guessName = name); <-- ERROR
                System.out.println("Right on! ");


        }

    }

What have I done wrong?

Upvotes: 1

Answers (11)

Carlos Valenzuela

Reputation: 834

The strings must be compared using the equals method.

Upvotes: 0

krtek

Reputation: 26597

String comparison

You can't compare Strings like this. This will only compare the references. You must use the equals() method :

while (! guessName.equals(name));

A little explanation : http://www.zparacha.com/java-string-comparison/

Variable redeclaration

There is another error in your code, you try to redeclare guessName inside the loop. You must declare guessName only once outside of the loop (ie before the do {).

General mistakes

Thirdly, there's a some other errors in your code. I think all of them were pointed out in the others answer, but I'll do a quick list :

if (guessName = name); This is a useless statement as is, you must open a block : if(condition) { statement; }
Same line, your doing an assignment, not a comparison, and like said, with String you must use .equals()
The System.out.println() won't be executed when you think. Re-read the doc about do { } while() loop until you really understand them.

My advise : read carefully the error message of your compiler and read some doc before writing code.

Upvotes: 3

tonio

Reputation: 10541

Here is what the javac compiler says:

GuessName.java:26: guessName is already defined in main(java.lang.String[])
        String guessName = guess.next(); //<-- ERROR
               ^
GuessName.java:32: incompatible types
found   : java.lang.String
required: boolean
              if (guessName = name);// <-- ERROR
                    ^
2 errors

For the first one, you should not declare another local variable: drop the String. For the second, use .equals to compare String objects, as the doc says.

You will obtain something like that:

...
//Recieve a guess
do {
  System.out.println("Please guess my name. Enter your guess here: ");
  guessName = guess.next(); //<-- FIXED
  //Create loop
} while (!guessName.equals(name)) //<-- FIXED

if (guessName.equals(name))// <-- FIXED
  System.out.println("Right on! ");
}
...

which works correctly.

Upvotes: 0

Morten Kristensen

Reputation: 7613

The line String guessName = guess.next(); needs to be changed to:

guessName = guess.next();

Because "guessName" is already defined earlier.

Additionally, when you compare strings you need to use the method equals and not the operator ==. So } while (guessName != name); should be:

} while (!guessName.equals(name));

And if (guessName = name); should be changed to:

if (guessName.equals(name))

Upvotes: 0

Swaranga Sarma

Reputation: 13423

Try this

public class GuessName {

        /**
         * @param args the command line arguments
         */

        public static final int C_Max_Trials = 10;

        public static void main(String[] args) {
            //Define correct name
            String name = "Morten";
            String guessName = null;

            //Create a scanner
            Scanner guess = new Scanner(System.in);

            //Recieve a guess
            do {
            System.out.println("Please guess my name. Enter your guess here: ");
            guessName = guess.nextLine(); <-- ERROR

            if(!guessName.equals(name))
            {
               System.out.println("Sorry, wrong guess, please enter another guess: ");
            }

            //Create loop
            } while (!guessName.equals(name)); <-- ERROR


              if (guessName.equals(name)) <-- ERROR
                System.out.println("Right on! ");


        }

    }

Upvotes: 0

Martin Klinke

Reputation: 7332

Among other things there is a wrong semicolon after the if:

if (name.equals(guessName))  //removed the semicolon and use .equals 
   System.out.println("Right on! ");

and it's an assignment instead of a comparison as other answers state by now.

Upvotes: 0

Andrzej Doyle

Reputation: 103797

That won't compile for a start - you declare String guessName on the third line of the main method, and then declare the same variable again within the do loop. You should simply use the name of the variable to assign to it:

guessName = guess.next();

Because of this error, presumably your IDE's compiler doesn't see the variable at all, so the subsequent lines that refer to guessName are also flagged as errors. Fixing this first line should clear those up, unless there's another problem lying there that I've missed.

Upvotes: 0

Vivek Goel

Reputation: 24150

you are comparing two objects. Not two string values. use equals

Upvotes: 0

Costi Ciudatu

Reputation: 38195

You're comparing references (well, with guessName = name, you're actually assigning a value to guessName). Use String.equals() instead of == and !=.

Upvotes: 0