Pojahns newbie thread

[Pojahn_M]

Status: ------

Hello.
First issue, I want to make a program that convert big letter to small. I have a method, but I get compile error.

class Pojahns

{
	public static void main (String[] args) throws Exception

	{

	java.util.Scanner	in = new java.util.Scanner (System.in);

	int tal1 = in.nextInt ();
	in.nextLine ();
	int tal2 = in.nextInt ();
	in.nextLine ();
	int max = (tal1 > tal2 ? tal1 : tal2);

	if (max >= 1 && max <= 10)
	{
		System.out.println ("Write three big letters");
		char c1 = (char) System.in.read ();
		System.in.read ();
		System.in.read ();
		char c2 = (char) System.in.read ();
		System.in.read ();
		System.in.read ();
		char c3 = (char) System.in.read ();

		char c4 = (char) c1 + 32;
		char c5 = (char) c2 + 32;
		char c6 = (char) c3 + 32;

		System.out.println ("The small letters are: " + c4 + c5 + c6);
	}

	else
	{
		System.out.print ("You wrote " + tal1 + " och " + tal2 + "\n");
	}

	}
}

And the error messege

C:\New\Pojahns.java:27: possible loss of precision
found   : int
required: char
		char c4 = (char) c1 + 32;
		                    ^
C:\New\Pojahns.java:28: possible loss of precision
found   : int
required: char
		char c5 = (char) c2 + 32;
		                    ^
C:\New\Pojahns.java:29: possible loss of precision
found   : int
required: char
		char c6 = (char) c3 + 32;
		                    ^
3 errors

Tool completed with exit code 1

How to fix this?

[sunde887]

What happens if you do (char)(c + 32)?

[Pojahn_M]

That fixed it, thanks.

[sunde887]

Your welcome. I may be wrong bit I believe the problem was that you were casting c to char then adding an int to it, which made it an int than setting a char to be an int.

[Pojahn_M]

sunde887 you are correct.

New issue: I am going to create a simple program.
You write a number, the program check if it is posetive or negative, if it is posetive, the program print that the number in negative, and then you write an number again and it chekcs again, and vise versa if the number is posetive, and you stop this endless loop if you write "0" (sans quotes).

Example how it would work:

Write a number:
5
5 is posetive.
Write a number:
6
6 is posetive.
Write a number:
-6
-6 is negative.
Write a number:
1
1 is posetive.
Write a number:
0
Program exit.

I cant figure out how I could make this. If/else would not work, becuse they wont loop. A while or do-while loop doesnt have alternative to check if is is this or that. Same goes for a for-loop. But my book want me to use some of these. So can someone give me tipps, how I can make a loop with alternatives?

[sunde887]

Do you know how to set up an infinite loop? The entire solution falls into using that and break and if else statements.

[Pojahn_M]

Alright, I took your suggestion, using a loop and else/if statement.
But it wont loop, you write a number, the program print whether its posetive or negative, then it ends. Here is code:

class Pojahns

{
	public static void main (String[] args) throws Exception

	{

	java.util.Scanner	in = new java.util.Scanner (System.in);

	System.out.print ("Write a number: ");
	int tal;
	System.out.println ();

	do
	{
	tal = in.nextInt ();

		if (tal > 0)
		{
			System.out.println (tal + " is posetive.");
		}

		else if (tal < 0)
		{
			System.out.println (tal + " is negative.");
		}
	}
	while (tal == 0);

	System.out.println ("You wrote \"0\", the program will exit.");

	}
}

Also I cant figure out how break statement will be useful here.
Most important, why wont it loop?

EDIT: Never mind, I got it working with a for loop:

class Pojahns

{
	public static void main (String[] args) throws Exception

	{

	java.util.Scanner	in = new java.util.Scanner (System.in);

	System.out.print ("Write a number: ");
	int tal;
	System.out.println ();

	for ( ; ; )
	{
	tal = in.nextInt ();

		if (tal > 0)
		{
			System.out.println (tal + " is posetive.");
		}

		else if (tal < 0)
		{
			System.out.println (tal + " is negative.");
		}

		else if (tal == 0)
		{
			System.out.println ("You wrote \"0\", the program will exit.");
			break;
		}

	}




	}
}

My first method, using do, could have worked if I changed while (tal == 0) to while (tal != 0). So yeah, both work in this case. :p

[sunde887]

Im glad you worked it out, I was just about to post that your condition is wrong.

You could also do something like

while(true){
  tal = in.nextInt();
  if(tal < 0){
    //print that its neg
  }
  else if(tal > 0){
    //print that its pos
  }
  else if(tal == 0){
    break;
  }
}

[Pojahn_M]

Im glad you worked it out, I was just about to post that your condition is wrong.

You could also do something like

[B]while(true)[/B]{
  tal = in.nextInt();
  if(tal < 0){
    //print that its neg
  }
  else if(tal > 0){
    //print that its pos
  }
  else if(tal == 0){
    break;
  }
}

thats an other way to make a endless loop:) Thanks for info. As you see I am new to java, and I love it, its so fun D:D

[Pojahn_M]

class Testclass

{
	public static void main (String[] args) throws Exception

	{

	java.util.Scanner	in = new java.util.Scanner (System.in);

	char tal1;

	for ( ; ; )
	{
		[B]System.out.print ("Write a character: ");[/B]
		tal1 = (char) System.in.read ();
		int tal2 = (int) tal1;

		if (tal2 == 113)
		{
			System.out.println ("Program exit");
			break;
		}
		else if (tal2 == 81)
		{
			System.out.println ("Program exit");
			break;
		}
		else
		{
			continue;
		}

	}

	System.out.println ("Loop end");


	}
}

This line in my code above:
System.out.print ("Write a character: ");
It get played 3 times(not the first time), I got now clue why. Solution?

[sunde887]

how do you know it isn't being printed the first time? Show me some sample input/output of the program being executed.

[Pojahn_M]

how do you know it isn't being printed the first time? Show me some sample input/output of the program being executed.

it is being printed, but not three times.

[sunde887]

are you entering a value equal to (int)'s' ?

[Pojahn_M]

yeah, numbers. But never mind this, I have started with array(fixed) now.

[Pojahn_M]

I have a question about array. There is one part in this chapter that i dont understand. Help me explain what it does in these two situations:

Example 1:

int v1 = new int[10];
int v2 = new int[10];
v1 = v2; //WTF does this mean?

Example 2:

int[] v1 = { 1, 3, 5, 7, 9 };
int[] v2 = { 2, 4, 6, 8, 10 };
v1 = v2; //Same question here

[sunde887]

What do you think it does?

Say you created a class of your own and did something similar

public class Car{
  Color col;
  public Car(Color col){
    this.col = col;
  }
  public static void main(String[] args){
    Car c1 = new Car(Color.red);
    Car c2 = new Car(Color.black);
    c1 = c2;
  }
}

What do you think that does?

Also, what happens if you print the arrays after the thing you don't understand?

System.out.println("This is v1");
for(int i = 0; i < v1.length; i++){
  System.out.print(v1[i] + ", ");
}
System.out.println();
System.out.println("This is v2");
for(int i = 0; i < v2.length; i++){
  System.out.print(v2[i] + ", ");
}

put this code after example 2 in your questions


Also, if you did

int i = 3;
int j = 4;
i = j;

What would be the new values of i and j?

To help even more

int[] v1;
int[] v2 = { 1, 3, 5, 7, 9 };
v1 = v2;

What would that do?

[Pojahn_M]

I see, so v1 = v2 means that all the values from v2 get copied to v1 values.

int[] v1 = { 1, 3, 5, 7, 9 };
int[] v2 = { 2, 4, 6, 8, 10 };
v1 = v2

//The new v1:
//v1[0] is now 2
//v1[1] is now 3
//v1[2] is now 4
//v1[3] is now 5
//v1[4] is now 6

Thx once again.

[sunde887]

Pretty much, however; I could be wrong(but I don't think I am) it really just makes the two things refer to the same object on the heap. If I am wrong I hope someone will correct me. Glad you figured it out, post back if you get stuck on anything else.

[Pojahn_M]

In this code:

class Pojahns

{
	public static void main (String[] args)// throws Exception

	{
		java.util.Scanner	in = new java.util.Scanner (System.in);

		int a = 5;
		int b = 2;

		int biggest = max(a,b);

		System.out.println (biggest);
	}

	public static int max (int number1, int number2)
	{
		return (number2 > number1) ? number2 : number1;
	}
}

Can you please explain how the return works here?
Hmm how should I explain my concern........
It seems that the program return number1, and its being printed in System.out.println (biggest);. But how? biggest value is from max, not number1. I dont even know how to explain. Please help.

[sunde887]

If number 2 is larger it returns number 2 otherwise it returns 1.

Try setting biggest to max(b, a); and see what happens.