LESSON THREE LOOPS. Open in Notepad++ for line numbers

// Steve Eilertsen
// Program does not run. All input from JOptionPane is String.
// Line 29 gives an error because we are trying to store a String into
// an integer variable.

import javax.swing.JOptionPane;

public class Loops 
{

   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      int times = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello " + x);
      }

   } // end main
   
} // end class


==============================================

// This program runs because the JOptionPane String variable in line 67
// is parsed and stored in an integer in line 69

import javax.swing.JOptionPane;

public class Loops2 
{

   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
	  // The for method has three arguements (parameters separated by semi colons)
	  // 1) Declare and initialise x.
	  // 2) The condition follows. If true, the loop will execute.
	  // 3) The value of x is increasd by one.
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello " + x);
      }

   } // end main
   
} // end class


===============================================

// Adds a while loop. This program does not run because it wants to use 
// the variable x which has not been declared.

import javax.swing.JOptionPane;

public class Loops3 
{

   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
	  // x below is local to the for loop ONLY.
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello for loop: " + x);
      }
      
	  // x no longer exists.
      while(x < times)
      {
      
      
      }

   } // end main
   
} // end class


===========================================

// This program runs because x has been declared in line 174.
// The variable x is declared an integer and initialised to zero.
// At this point the while loop does not do anything but it does run.
// Unfortunaley it is an infinate loop because the condition is never met.
// The value x is always smaller than the variable "times" and therefore the 
// loop continues to run indefinatley.

import javax.swing.JOptionPane;

public class Loops4 
{

   
   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello for loop: " + x);
      }
      
	  // We need to declare x so that the while loop can use it
      int x = 0;
      
	  // This is an infinate loop.
      while(x < times)
      {
      
      
      }

   } // end main
   
} // end class


=============================================

// Here the while loop is not infinite. The value of x is increased in line 231,
// so the condition is met and the loop terminates.

import javax.swing.JOptionPane;

public class Loops5 
{

   
   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello for loop: " + x);
      }
      
      int x = 0;
      
	  // This loop does terminate because x increases in size
	  // until the condition is met
      while(x < times)
      {
      
         x++;
      }

   } // end main
   
} // end class



===============================================

// The while loop finally does something

import javax.swing.JOptionPane;

public class Loops6 
{

   
   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello for loop: " + x);
      }
      
      int x = 0;
      
      while(x < times)
      {
         System.out.println("hello while loop: " + x);
         x++;
      }

   } // end main
   
} // end class


=============================================

// Another for loop is coded using char but it does not run.
// This is because the variable x used for the while still exists - it is local
// to the whole main method. Therefore a second x cannot be declared by the
// new for loop.

import javax.swing.JOptionPane;

public class Loops7 
{

   
   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello for loop: " + x);
      }
      
      int x = 0;
      
      while(x < times)
      {
         System.out.println("hello while loop: " + x);
         x++;
      }
      
	  // the variable x still exists and cannot be declared a second time.
      for(char x = 'A'; x < 'Z'; x++)
      {
      
         System.out.println("char");
      }

   } // end main
   
} // end class


============================================

// This runs. The for loop loops from "A" to "Z". The variable y increases
// each time by one, moving from letter to letter in the alphabet

import javax.swing.JOptionPane;

public class Loops8 
{

   
   public static void main(String[]args ) 
   {
      JOptionPane.showMessageDialog(null, "hello world"   );
      
      String myName = JOptionPane.showInputDialog(null, "Input your name?"   );
      myName = myName.toUpperCase( );
      
      if (myName.equals("STEVE"))
      {
      
         System.out.println("Bingo");
      
      }
      
      System.out.println("Good morning " + myName);
      
      String timesSt = JOptionPane.showInputDialog(null, "How many times must the loop run?"   );
      
      int times= Integer.parseInt(timesSt);
      
      for(int x = 0; x < times; x++)
      {
         System.out.println("hello for loop: " + x);
      }
      
      int x = 0;
      
      while(x < times)
      {
         System.out.println("hello while loop: " + x);
         x++;
      }
      
	  // Loop starts at A and terminates with Z
      for(char y = 'A'; y <= 'Z'; y++)
      {
      
         System.out.println("Char: " + y);
      }

   } // end main
   
} // end class


========================================

FINAL OUTPUT
============

 ----jGRASP exec: java Loops8
Bingo
Good morning STEVE
hello for loop: 0
hello for loop: 1
hello for loop: 2
hello for loop: 3
hello for loop: 4
hello while loop: 0
hello while loop: 1
hello while loop: 2
hello while loop: 3
hello while loop: 4
Char: A
Char: B
Char: C
Char: D
Char: E
Char: F
Char: G
Char: H
Char: I
Char: J
Char: K
Char: L
Char: M
Char: N
Char: O
Char: P
Char: Q
Char: R
Char: S
Char: T
Char: U
Char: V
Char: W
Char: X
Char: Y
Char: Z

 ----jGRASP: operation complete.