CSC 313 Java Control Structures

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CSC 313 Java Control Structures
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Selection Structures

• Java has a sequence structure built-in
• Java provides three selection structures
• if
• if/else
• switch
• Java provides three repetition structures
• while
• do/while
• do
• Each of these words is a Java keyword

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Decision Making

• if control structure
• Simple version in this section, more detail later
• If a condition is true, then the body of the if
  statement executed
• 0 interpreted as false, non-zero is true
• Control always resumes after the if structure
• Conditions for if structures can be formed using
  equality or relational operators (next slide)
• if ( condition )
• statement executed if condition true
• No semicolon needed after condition
• Else conditional task not performed

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The if Statement

• The if statement, in its simplest
  configuration, takes this form
• if (expression)
• statement next statement

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The syntax of the if/else Statement
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The if Statement without else
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The else Clause
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An if Statement with an else clause
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An if Statement with an else if and else clause
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Nested if Statements
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The Conditional Operator

• The conditional operator is a notational variant
  on certain forms of the if-else statement
• Also called the ternary operator or arithmetic if
• The following examples are equivalent
• if (n1 gt n2) max n1
• else max n2
• vs.
• max (n1 gt n2) ? n1 n2
• The expression to the right of the assignment
  operator is a conditional operator expression
• If the Boolean expression is true, then the
  expression evaluates to the value of the first
  expression (n1), otherwise it evaluates to the
  value of the second expression (n2)

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The while Repetition Structure

• Repeat action while condition remains true

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The Syntax of the while loop
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While Loop
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Statement Blocks

• In general, wherever you can have one executable
  statement in Java, you can replace it with a
  block of statements enclosed between braces
  instead.
• if(expression)
• statement 1
• statement 2
• ...

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The switch Statement
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The switch Statement no break
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Loop Instructions
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while loop

• The while loop
• int i 0
• final int n 100
• while ( i lt n )
• System.out.println( i )
• i i 1
• prints 0,1,,99.

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do while loop

• The do while loop
• int i 0
• final int n 100
• do
• System.out.println( i )
• i i 1
• while ( i lt n )
• prints 0,1,,99.

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for loops
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Labeled continue Statement

• Where you have nested loops, there's a special
  form of the continue statement that enables you
  to stop executing the inner loop-not just the
  current iteration of the inner loop-and continue
  at the beginning of the next iteration of the
  outer loop.
• In general, you can use the labeled continue to
  exit from an inner loop to any enclosing outer
  loop, not just the one immediately enclosing the
  loop containing the labeled continue statement.

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Labeled continue illustrated

• public class Factorial
• public static void main(String args)
• long limit 20 // Calculate
  factorial of integers up to this value
• long factorial 1 // Calculate
  factorial in this variable
• // Loop from 1 to the value of limit
• OuterLoop
• for(int i 1 i lt limit i)
• factorial 1 //
  Initialize factorial
• for(int j 2 j lt i j)
• if(i gt 10 i 2 1)
• continue OuterLoop // Transfer
  to the outer loop
• factorial j
• System.out.println("!" i " is "
  factorial)

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the break Statement in a Loop
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Variable Scope

• A variable doesn't exist before its declaration,
  so you can only refer to it after it has been
  declared.
• It continues to exist until the end of the
  block in which it is defined, and that includes
  any blocks nested within the block containing
  its declaration.

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Variable Scope Illustrated
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End of Loopy Java!
Have a Nice Weekend!!