while loop with a decrementing counter

[tolkienarda]

hi all
i have a with my counter that starts at a value then for each step through the loop it should go down by one. ok the trial data i have when i run this program, and i have checked and rechecked it to make sure that the test data has the expected values

i=3
revline[0]=a
[1]=s
[2]=d
[3]=f

    		System.out.println(i);
	    	while(i>=0)
	    	{
	    		System.out.print(revline[i]);
	    		i--;
	    		System.out.print(i);
	    	}

output:
3

Process completed.
if I move the second System.out.prin t(i); above the i--; then it will print a 3 so I think that the i--; line is incorect but I tried i = i - 1; and that didn't work either so I am at a total loss, the remainder of my code is below,
this is a homework assignment and I am not trying to cheat just figure out my error, anyway the assignment is to get a string from a user then print it reversed

/**
 * @(#)asg5.java
 *
 * asg5 application
 *;
 * @author 
 * @version 1.00 2007/9/24
 */
 import java.util.*;
public class asg5 {
    static Scanner console = new Scanner(System.in);
    public static void main(String[] args) {
    	String line;
    	Boolean rev;
    	System.out.println("Enter a line of text 'q' to exit");
    	line = console.nextLine();
    	rev = recRev(line, 0);
    	
    	
    }
    public static Boolean recRev(String line, int pos){
    	int length, i;
    	char[] revline = new char[50];
    	length = line.length();
    	i=length - 1;
		
    	if (length>50)
    	{
    		return false;
    	}
    	if (pos<length)
    	{
    		revline[pos] = line.charAt(pos);
    		pos = pos + 1;
    		recRev(line, pos);
    	}else{
    		System.out.println(i);
	    	while(i>=0)
	    	{
	    		System.out.print(revline[i]);
	    		i--;
	    		System.out.print(i);
	    	}
    	}
    	return true; 
    }
}

thanks
eric

[Nepomuk]

hi all
i have a with my counter that starts at a value then for each step through the loop it should go down by one. ok the trial data i have when i run this program, and i have checked and rechecked it to make sure that the test data has the expected values

i=3
revline[0]=a
[1]=s
[2]=d
[3]=f

    		System.out.println(i);
	    	while(i>=0)
	    	{
	    		System.out.print(revline[i]);
	    		i--;
	    		System.out.print(i);
	    	}

output:
3

Process completed.
if I move the second System.out.prin t(i); above the i--; then it will print a 3 so I think that the i--; line is incorect but I tried i = i - 1; and that didn't work either so I am at a total loss, the remainder of my code is below,
this is a homework assignment and I am not trying to cheat just figure out my error, anyway the assignment is to get a string from a user then print it reversed

/**
 * @(#)asg5.java
 *
 * asg5 application
 *;
 * @author 
 * @version 1.00 2007/9/24
 */
 import java.util.*;
public class asg5 {
    static Scanner console = new Scanner(System.in);
    public static void main(String[] args) {
    	String line;
    	Boolean rev;
    	System.out.println("Enter a line of text 'q' to exit");
    	line = console.nextLine();
    	rev = recRev(line, 0);
    	
    	
    }
    public static Boolean recRev(String line, int pos){
    	int length, i;
    	char[] revline = new char[50];
    	length = line.length();
    	i=length - 1;
		
    	if (length>50)
    	{
    		return false;
    	}
    	if (pos<length)
    	{
    		revline[pos] = line.charAt(pos);
    		pos = pos + 1;
    		recRev(line, pos);
    	}else{
    		System.out.println(i);
	    	while(i>=0)
	    	{
	    		System.out.print(revline[i]);
	    		i--;
	    		System.out.print(i);
	    	}
    	}
    	return true; 
    }
}

thanks
eric

Hi Eric!

I can't see the error in your code right now, but normally for that sort of job you'd use a for-loop like this:
[CODE=java]
for(int i=0; i>=0; i--) // if you want to define i before, use for(; i>=0; i--)
{
// ...
}
[/CODE]Also, why don't you create the char array with exactly the same amount of chars as the String has?

Greetings,
Nepomuk

[stack]

Nepomuk is right!

Just create an array of chars and then store in it all the chars
of the string that the user enters. Then the only thing left is to print
the array on the screen but starting from the last position.
You 'll save yourself from a lot of typing :-)))

Cheers

[Nepomuk]

Just create an array of chars and then store in it all the chars
of the string that the user enters.

Read the String API to find methods, that will be very useful doing that job.

Greetings,
Nepomuk

[tolkienarda]

thanks you guys

here is how i finaly did it

 import java.util.*;
public class asg5 {
	
    static Scanner console = new Scanner(System.in);
    public static void main(String[] args) {
    	String line;
    	String again;
    	Boolean rev;
    	int length;
    	int i;
    	System.out.println("Enter a line of text");
    	line = console.nextLine();
    	length = line.length();
    	i=length - 1;
    	rev = recRev(line, i);

    	
    	
    }
    public static Boolean recRev(String line, int i){  
    	if (i>=0)
    	{
    		System.out.print(line.charAt(i));
	    	i--;
    		recRev(line, i);
    	}
    	return true;
    }
}

i read the problem from my textbook again and all it says is use a recursive function to print it backward and so i did
but now i am having a new problem. i want to ask the user if they want to do it over again. so my plan was to ask the user and if they enter yes recall the main() function, i am having some problems with my if statement not sure what is wrong with it but if one of you could take a look that would be helpful

the below code is located at the end of my main() function.
when i print the again var it prints a y but then won't go into my if statement

        String again;
    	System.out.println("\n would you like to go again(y/n)");
    	again = console.next();
    	System.out.println(again);
    	if(again == "y")
    	{
    		System.out.println("i cant get here");
    		main(args);
    	}

When i comment the if statement and the curly braces it prints the "i cant get here" and recalls the function but won't allow me to enter more text. it just reprints the
Enter a line of text
then the
would you like to go again(y/n)
and it will allow me to input here and when i do it prints
i cant get here
then starts over again

here is all of the code together with the if statement not commented out

thanks for all the help

/**
 * @(#)asg5.java
 *
 * asg5 application
 *;
 * @author 
 * @version 1.00 2007/9/24
 */
 import java.util.*;
public class asg5 {
	
    static Scanner console = new Scanner(System.in);
    public static void main(String[] args) {
    	
    	String line;
    	String again;
    	Boolean rev;
    	int length;
    	int i;
    	System.out.println("Enter a line of text");
    	line = console.nextLine();
    	length = line.length();
    	i=length - 1;
    	rev = recRev(line, i);
    	System.out.println("\n would you like to go again(y/n)");
    	again = console.next();
    	System.out.println(again);
   		if (again == "y")
    	{
    		System.out.println("i cant get here");
    		main(args);
    	}
    	
    	
    }
    public static Boolean recRev(String line, int i){  
    	if (i>=0)
    	{
    		System.out.print(line.charAt(i));
	    	i--;
    		recRev(line, i);
    	}
    	return true;
    }
}

eric

[tolkienarda]

ok so i just figured out why my if didn't work i needed the str.equals("y") function. and i kinda gave up on the recursive main function though i would still like to know if it works. anyway i put my code below the declarations into a loop and it works except i am having the save problem that i can't reinput my line variable, not sure why. if any one knows it would be helpful, i read the scanner class documentation and couldn't find anything about it in there, the part that confuses me the most is that it allows me to input the again variable.

thanks for any ideas or comments

eric

[Nepomuk]

ok so i just figured out why my if didn't work i needed the str.equals("y") function. and i kinda gave up on the recursive main function though i would still like to know if it works. anyway i put my code below the declarations into a loop and it works except i am having the save problem that i can't reinput my line variable, not sure why. if any one knows it would be helpful, i read the scanner class documentation and couldn't find anything about it in there, the part that confuses me the most is that it allows me to input the again variable.

thanks for any ideas or comments

eric

Well done for figuring out the problem yourself! I do however have a recommendation, that will make things easier:

Whenever you want to have something, that should (may) be used more than once, write an own method for it. That makes it much easier to repeat everything - you could have something like this:
[CODE=java]
boolean continue = false;
do
{
recursiveFuncti on(args);
System.out.prin tln("Again?");
if(scanner.next ().equals("y"))
continue = true;
} while(continue)
[/CODE]That should also allow you to reset all values that aren't final (including the line variable I hope).

Greetings,
Nepomuk

[r035198x]

Well done for figuring out the problem yourself! I do however have a recommendation, that will make things easier:

Whenever you want to have something, that should (may) be used more than once, write an own method for it. That makes it much easier to repeat everything - you could have something like this:
[CODE=java]
boolean continue = false;
do
{
recursiveFuncti on(args);
System.out.prin tln("Again?");
if(scanner.next ().equals("y"))
continue = true;
} while(continue)
[/CODE]That should also allow you to reset all values that aren't final (including the line variable I hope).

Greetings,
Nepomuk

Except that continue is a keyword so the compiler won't like any of that.

[Nepomuk]

Except that continue is a keyword so the compiler won't like any of that.

Ah, true, then call the boolean "continueWithWh ateverYouAreDoi ng" or "dontStop" or something like that. But year, continue is a codeword... which makes me think of being evil and doing it like this:
[CODE=java]
while(true)
{
recursiveFuncti on(args);
if(scanner.next ().equals("y") continue;
break;
}
[/CODE]which looks pretty awful, I find. (But it should work! ^^)

Greetings,
Nepomuk

[tolkienarda]

thank you all for your help just one more quick question

is it possible to recall the main() function
i don't need it for this program but it may be useful sometime in the future

eric

[r035198x]

thank you all for your help just one more quick question

is it possible to recall the main() function
i don't need it for this program but it may be useful sometime in the future

eric

Don't try to do that at all. Always look for an alternative design.

[tolkienarda]

hmm i am still having a problem
i still cannot input my string that is to be reversed.
and my loop appears to be infinite, i am not sure if that semi colon behind my while statement is correct but i got build errors without it
here is my entire main() function

    public static void main(String[] args) {
    	
    	String line;
    	Boolean cont = false;
    	Boolean rev;
    	int length;
    	int i;
    	do
    	{
	    	System.out.println("Enter a line of text");
	    	line = console.nextLine();
	    	length = line.length();
	    	i=length - 1;
	    	rev = recRev(line, i);
	    	System.out.println("\n would you like to go again(y/n)");
	    	if(console.next().equals("y"))
	    		cont = true;
    	} while(cont);
    }

Output
[CODE]
Enter a line of text
asdf
fdsa
would you like to go again(y/n)
y
Enter a line of text

would you like to go again(y/n)
n
Enter a line of text

would you like to go again(y/n)
[CODE]

and there is no pause for me to input text after the "Enter a line of text" line it just prints the " would you like to go again(y/n)"

eric

[tolkienarda]

Don't try to do that at all. Always look for an alternative design.

Ok

thanks
eric

[JosAH]

[CODE=java]
while(true)
{
recursiveFuncti on(args);
if(scanner.next ().equals("y") continue;
break;
}
[/CODE]which looks pretty awful, I find. (But it should work! ^^)

Duh;

[code=java]
do {
recursiveFuncti on(args);
}
while (scanner.next() .equals("y"));
[/code]

kind regards,

Jos

[Nepomuk]

Duh;

[code=java]
do {
recursiveFuncti on(args);
}
while (scanner.next() .equals("y"));
[/code]

kind regards,

Jos

Year, but that doesn't contain continue! ^^