Structured Programming

1
Structured Programming

• Structured Programming is writing a program in
  terms of only 3 basic control structures
• sequence
• selection
• repetition
• We have already seen two of these.

2
Lots of Choices

• import cs1.Keyboard
• public class Testing
• public static void main( String args)
• System.out.println("Enter an integer between 1
  and 5")
• int num Keyboard.readInt()
• if (num 1)
• System.out.println("It's a one")
• else if (num 2)
• System.out.println("It's a two")
• else if (num 3)
• System.out.println("It's a three")
• else if (num 4)
• System.out.println("It's a four")
• else if (num 5)
• System.out.println("It's a five")
• else
• System.out.println("Number not in range")

3
The Switch Statement

• switch(num)
• case 1
• System.out.println("It's a one")
• break
• case 2
• System.out.println("It's a two")
• break
• case 3
• System.out.println("It's a three")
• break
• case 4
• System.out.println("It's a four")
• break
• case 5
• System.out.println("It's a five")
• break
• default
• System.out.println("Number not in range")

4
Repetition---the while loop

• public static void main( String args)
• System.out.println("Enter an integer number
  between 1 and 5")
• int num Keyboard.readInt()
• while(num lt 1 num gt 5)
• System.out.println("Number not in range---try
  again")
• num Keyboard.readInt()
• System.out.print("\nThanks, the number ")
• if (num 1)
• System.out.print("one")
• else if (num 2)
• System.out.print("two")
• else if (num 3)
• System.out.print("three")
• else if (num 4)
• System.out.print("four")
• else
• System.out.print("five")
• System.out.println(" is a great choice")

5
The while Loop

• The while loop in Java is a pre-test loop. The
  test of the condition is done at the beginning of
  the loop.
• The loop continues as long as the condition is
  true. As soon as the condition becomes false,
  the loop stops and the next statement is
  executed.
• If the condition is false the first time it is
  tested, the loop is never executed at all.

6
Infinite Loops

• The loop control variable needs to be initialized
  at the beginning of the loop, and tested each
  time the loop is executed.
• Somewhere in the loop there must be something
  that can change the value of the loop control
  variable.
• If there is not, we have an infinite loop which
  will continue going round and round until you
  stop it from outside.
• If this happens in BlueJ, close the BlueJ window
  and start it up again. Then go to the editor and
  fix the problem.

7
Logical Operators

• Boolean expressions can also use the following
  logical operators
• ! Logical NOT
• Logical AND
• Logical OR
• They all take boolean operands and produce
  boolean results
• Logical NOT is a unary operator (it has one
  operand), but logical AND and logical OR are
  binary operators (they each have two operands)

8
Getting a Menu Choice

• public int getMenuChoice()
• int choice 0
• while (choice lt 1 choice gt 4)
• System.out.println("\n\nChoose one from the
  menu below")
• System.out.println("1. Yes")
• System.out.println("2. No")
• System.out.println("3. Maybe")
• System.out.println("4. Exit")
• int choice Keyboard.readInt()
• if (choice lt 1 choice gt 4)
• System.out.println("Choose a number
  between 1 and 4")
• return choice

9
Increment and Decrement Operators

• The increment and decrement operators are
  arithmetic and operate on one operand
• The increment operator () adds one to its
  operand
• The decrement operator (--) subtracts one from
  its operand
• The statement
• count
• is essentially equivalent to
• count count 1

10
Increment and Decrement Operators

• When used in a larger expression, the prefix and
  postfix forms have a different effect
• In both cases the variable is incremented
  (decremented)
• But the value used in the larger expression
  depends on the form

11
Assignment Operators

• There are many assignment operators, including
  the following