Ch 3 Control Structures

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Ch 3 Control Structures

• 3.1 Three Essential Structures
• 3.2 Conditions
• 3.3 Selection and Repetition
• 3.4 Nested and Multiple-Alternative Selection
  Structures
• 3.5 The switch statement for Multiple Alternatives

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3.1 Three Essential Structures

• Sequential
• code executes in sequence (line 1 to line n)
• do deviations
• Selection
• chooses one of many alternative paths
• only one path is chosen and executed
• Repetition
• same code is executed repeatedly

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3.2 ConditionsIf statement

• Decisions are made through the use of the if
  statement.
• Syntax
• if (expression) statements

if (age gt 21) cout ltlt "Cheers!"
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3.2 ConditionsIf...else statement

• Syntax
• if (expression) statements
• else statements

• if (age gt 21)
• cout ltlt "Cheers!"
• else
• cout ltlt "Soda anyone?"

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3.2 ConditionsRelational Operators

• Use relational operators in your expressions
• gt greater than
• lt less than
• gt greater than or equal
• lt less than or equal
• equal to
• ! not equal
• A Boolean expression must evaluate to either true
  or false.

3 4 gt 5 2 evaluates to true (2 3 1) lt
4 2 / 9 evaluates to false 2 / 3 3
0 evaluates to true
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3.2 ConditionsLogical Operators

• Use logical operators in your expressions
• AND (true if both arguments are true)
• OR (true if either argument is true)
• ! NOT (true if single argument is false)
• Logical expressions must evaluate to true or
  false.

1 3 evaluates to true 1 lt 3 4 gt
6 evaluates to true 5 1 gt 2 !0 evaluates
to true
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3.2 Conditionsif example
include ltiostreamgt using namespace std int
main() char achar cout ltlt "Enter a
alphabetic character " cin gtgt achar if
(achar 'a' achar 'A' achar
'e' achar 'E' achar 'i'
achar 'I' achar 'o' achar
'O' achar 'u' achar 'U')
cout ltlt "You entered a vowel. Thanks!" ltlt endl
ltlt endl
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3.2 Conditionsif example Continued
else cout ltlt "You entered a consonant.
Thanks!" ltlt endl ltlt endl
return (0)
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3.2 ConditionsDemo Examples

• Show examples of if, if...else
• ex 1. Given a test score, what is the letter
  grade equivalent
• ex 2. Given a character, display it in the
  opposite case
• ex 3. Given a character, display the preceding
  and following characters

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3.3 Selection and Repetition

• Single branch
• if (expression) statements
• Two-way branch
• if (expression)
• statements
• else
• statements

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3.4 Nested and Multi-branch Selectionsif...else
if...else

• if statements can and often are nested.
• Syntax
• if (expression1) statements
• else
• if (expression2)
• statements
• else
• statements

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3.4 Nested and Multi-branch Selectionsif...else
if...else Continued

• Rewrite the following if using a nested if

if (age gt 21 wantDrink 'Y') //
serve drink else // serve soda or
nothing
if (age gt 21) if (wantDrink 'Y') //
serve drink else // do not serve drink
else // serve soda
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3.4 Nested and Multi-branch Selectionsif...else
if...else Continued

• if (expression1)
• statements
• else if (expression2)
• statements
• else
• if (expression3)
• statements
• else
• if (expression4)
• statements

Notice the diagonal effect. Not cool!
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3.4 Nested and Multi-branch Selectionsif...else
if...else Continued

• Regain your coolness with an if...else if...else
  statement

• if (expression1) statements
• else if (expression2) statements else
  if (expressionN)
• statements
• else statements

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3.4 Nested and Multi-branch Selectionsif...else
if...else Continued

• Show examples
• If I were a rich man.... (NOT!)
• ex 1. Display menu of choices.
• ex 2. Display final course grade based on current
  class average.
• ex 3. Determine if given number is between three
  separate ranges. Take different action for each
  range.

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3.5 The switch Statement

• To switch or not to switch? That is the question.
• switch (expression) case constant_1
  statements breakcase constant_n
  statements breakdefault statements
  break

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3.5 The switch StatementExamples

• Show examples
• ex 1. Display a menu of choices (const, enum)
• ex 2. Determine if entered character is a vowel
  or consonant