CONTROL STRUCTURES (MULTI-WAY SELECTION)

1
CONTROL STRUCTURES(MULTI-WAY SELECTION)
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MULTI-WAY SELECTION

• EXTENDED IF-ELSE
• Used to select exactly one task out of multiple
  tasks (or possibly none)
• Unlike a series of ifs evaluation stops once
  one relational expression evaluates as true
  (others are skipped)
• Always does on less evaluation than a series of
  ifs
• Well planned implementation provides for
  efficiency most common choice is listed first

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MULTIPLE SELECTION

• EXTENDED IF-ELSE - SIMPLE
• if ( relational expression(s) )
• statement
• else
• if ( relational expression(s) )
• statement
• else
• if ( relational expression(s) )
• statement
• else
• statement

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MULTI-WAY SELECTION

• EXTENED IF-ELSE - COMPOUND
• if ( relational expression(s) )
• statement
• statement(s)
• else
• if ( relational expression(s) )
• statement
• statement(s)
• else
• if ( relational expression(s) )
• statement
• statement(s)

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MULTI-WAY SELECTION

• RULES
• 1. First statement(s) will be executed if and
  only if the evaluation of the relational
  expression(s) is/are true.
• 2. Second statement(s) will be executed if and
  only if the evaluation of the first relational
  expression(s) is/are false and if and only if
  the evaluation of the second relational
  expression(s) is/are true.
• 3. Same progression as 1 and 2 for all levels
  that exist.
• Note This process does not have to end with
  two, three or four selections, but can continue
  for as many selections as needed.

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MULTIPLE SELECTION

• EXAMPLES
• if (numStudentslt 6)
• salary hours CLUSTER_RATE
• else
• if (numStudents lt 12)
• salary hours LIMITED_RATE
• else
• salary hours FULL_RATE

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MULTIPLE SELECTION

• if (temperature gt 85)
• cout ltlt Go Swimming ltlt endl
• else
• if (temperature gt 70)
• cout ltlt Play Tennis ltlt endl
• cout ltlt Wear white! ltlt endl
• else
• if (temperature gt 32)
• cout ltlt Play Football ltlt end
• else
• if (temperature gt 10)
• cout ltlt Go Skiing ltlt endl
• else
• cout ltlt Go Bowling ltlt endl

• EXAMPLES
• if (temperature lt 10)
• cout ltlt Go Bowling ltlt endl
• else
• if (temperature lt 32)
• cout ltlt Go Skiing ltlt endl
• else
• if (temperature lt 70)
• cout ltlt Play Football ltlt endl
• else
• if (temperature lt 85)
• cout ltlt Play Tennis ltlt endl
• cout ltlt Wear white! ltlt endl
• else
• cout ltlt Go Swimming ltlt endl

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MULTI-WAY SELECTION

• NESTED IF-ELSE
• Situations where action is dependent upon two or
  more different conditions
• Examples

if (gender M) if (age lt MAX_AGE)
cout ltlt Male and under 67. ltlt endl else
cout ltlt Male and 67 or over. ltlt endl else
if (age lt MAX_AGE) cout ltlt Female and
under 67. ltlt endl else cout ltlt
Female and 67 or over. ltlt endl
if (savings gt DOLLAR_LIMIT) if (vacation gt
VACATION_LIMIT) cout ltlt Trip to Hawaii ltlt
endl else cout ltlt Vacation at local
ski resort. ltlt endl else cout ltlt Go camping
in mountains. ltlt endl
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MULTI-WAY SELECTION

• SWITCH
• Alternate form of multi-way selection
• Decision can only be made on integral or
  enumerated data types (bool, char, int)
• Does not work with strings or floating point
  numbers
• Only works when testing for specific values
• Does not work with ranges

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MULTI-WAY SELECTION

• SWITCH - SIMPLE
• switch (selector)
• case choice1 statement
• break
• case choice2 statement
• break
• case choice3 statement
• break
• case choice(n) statement

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MULTI-WAY SELECTION

• SWITCH WITH DEFAULT
• switch (selector)
• case choice1 statement
• break
• case choice2 statement
• break
• case choice(n) statement
• break
• default statement
• statement(s)

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MULTIPLE SELECTION

• SWITCH COMPOUND
• switch (selector)
• case choice1 statement
• statement(s)
• break
• case choice2 statement
• statemant(s)
• break
• case choice(n) statement
• statement(s)
• break
• default statement
• statement(s)

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MULTIPLE SELECTION

• RULES
• 1. Selector may only be an integral data type
  (int, char, bool, or enumerated).
• 2. Corresponding statement(s) is/are executed if
  choice is equal to the selector.
• 3. After corresponding statement(s) are
  executed if break is not present additional
  case statements are executed until a break is
  found or end of structure is found.
• 4. If no choice is equal to the selector, the
  switch is exited unless a default is available.

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MULTIPLE SELECTION

• EXAMPLES
• switch(category)
• case 1 cout ltlt Category One ltlt endl
• break
• case 2 cout ltlt Category Two ltlt endl
• break
• case n cout ltlt Category n ltlt endl
• break

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MULTI-WAY SELECTION

• int num1, num2, answer
• char choice
• cout ltlt "Enter two numbers, separated by a space
  "
• cin gtgt num1 gtgt num2
• cout ltlt endl ltlt endl
• cout ltlt "Perform which operation on the Numbers?"
  ltlt endl
• cout ltlt " a - Add" ltlt endl
• cout ltlt " s - Subtract" ltlt endl
• cout ltlt " m - Mulitply" ltlt endl
• cout ltlt " d - Divide" ltlt endl
• cout ltlt "Enter your choice from above " ltlt endl
• cin gtgt choice
• choice tolower (choice)
• switch (choice)
• case 'a answer num1 num2

• EXAMPLE

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MULTI-WAY SELECTION

• EXAMPLE
• char answer
• cout ltlt "Would you like to continue Y or
  N?" ltlt endl
• cin gtgt answer
• switch (answer)
• case 'Y'
• case 'y cout ltlt "You chose yes" ltlt endl
• cout ltlt "Way to go." ltlt endl
• break
• case 'N'
• case 'n cout ltlt "You chose no" ltlt endl
• cout ltlt "Not very positive." ltlt endl
• break
• default cout ltlt "You were suppose to choose
  Y or N." ltlt endl