Nested For Loops

1
Nested For Loops
2
Nested For Loops

• It is also possible to place a for loop inside
  another for loop.
• int rows, columns
•  
• for (rows1 rowslt5 rows)
• for (columns1 columnslt10 columns)
• System.out.print("")
• System.out.println ()

Outer Loop
Output

Inner Loop
3
Nested For Loops, Example 2

• //simple loop to print triangle using the
  character
• //Produces a right triangle with hypoten
  increasing to left
• public class while_numbers
• public static void main(String args)
• int rows, columns
• for (rows1 rowslt5 rows)
• for (columns1 columnsltrows columns)
• System.out.print("")
• System.out.print("\n")

Output
Outer Loop
Inner Loop
4
Nested For Loops using seconds and minutes

• Lets write a program in class to count number of
  seconds and minutes in one hour

5
Nested For Loops using seconds and minutes in one
hour

• //simple loop to print seconds and minutes in one
  hour
• public class while_numbers
• public static void main(String args)
• int seconds,minutes
• for (minutes0 minutes lt 59 minutes)
• for (seconds 0 seconds lt 59 seconds )
• System.out.println(minutes seconds)

6
Nested For Loops using seconds and minutes

• Lets write a program in class to count number of
  seconds and minutes and hours in one day

7
Nested For Loops using seconds and minutes in one
hour

• //simple loop to print seconds , minutes and
  hours in one day
• public class while_numbers
• public static void main(String args)
• int seconds,minutes, hours
• for (hours0 hourslt 23 hours)
• for (minutes0 minutes lt 59 minutes)
• for (seconds 0 seconds lt 59 seconds )
• System.out.println(hours minutes
  seconds)

8
Nested For Loops, Example 3

• public class Prog1
• //Produces a right triangle with hypoten
  increasing to right
• public static void main(String asd)
• final int MAX 8
• for(int j 0 j lt MAX j)//
• for(int k 0 k lt MAX - j k)//draw MAX - j
  blanks
• System.out.print(' ')
• for(int k 0 k lt j k)//draw remaining j
  columns as x's
• System.out.print('x')
• System.out.println()

9
Nested For Loops, multiplication table

• public class Program2a
• //Prelim to producing a multiplication table
• public static void main(String asd)
• for(int j 0 j lt 8 j)//label columns
• for(int k 0 k lt 9 k)
• System.out.print(k)
• System.out.println()
• final int HORIZ 6
• for(int j 1 j lt HORIZ j)//label
  horizontal
• System.out.print("\t" j)//tabs every 9
  columns
• System.out.println()

10
Nested For Loops, multiplication tableexample 2

• public class Prog2
• //Produces a multiplication table
• public static void main(String asd)
• final int HORIZ 6
• final int VERT 5
• for(int j 1 j lt HORIZ j)//label
  horizontal
• System.out.print("\t" j)//tabs every 9
  columns
• System.out.println()
• for(int j 1 j lt HORIZ 1 j)//draw line
• System.out.print("--------")
• System.out.println()
• for(int k 1 k lt VERT k)

11
Good Programming Practices

• Do not change the value of the counter variable
  in your loop.
• Do not attempt to manually adjust it to force an
  exit
• Can cause subtle errors that are difficult to
  catch
• Instead change your logic
• Do not put other expressions in the for control
  structure
• Manipulations of other variables should appear
  before or within the body of the loop depending
  on whether or not you want to repeat them
• Put a blank line before and after each major
  control structure
• Try to limit nesting to three levels, if possible
• More than three levels of indentation can get
  confusing
• Limit the for control header to one line if
  possible