CONTROL STRUCTURES (SELECTION)

PROGRAM COMPONENTS  SEQUENCE  Groups Of Sequential Steps  SELECTION  Making Choices  IF-THEN (one way)  IF-THEN-ELSE (two way or multi way)  SWITCH (multi way)  ITERATION(Looping)  Repeating Steps  WHILE – DO (top tested)  DO – WHILE (bottom tested)  FOR (fixed iteration)

BOOLEAN DATA TYPE  Two Values – true (1) or false (0)  Example: bool isOvertime = true; cout << “Is overtime “ << isOvertime << endl; isOvertime = false; cout << “Is overtime “ << isOvertime << endl;  Internal program value  Cannot be read in via keyboard entry  Only displayed as 1 or 0

BOOLEAN DATA TYPE  Boolean names should reflect true value For example: bool done = false; bool even = false; bool error = true;  Can be initialized with integer:  Using 0 intializes to false  Anything Else initializes to true  It is best to use values true or false

RELATIONAL / EQUALITY OPERATORS  Boolean expression is: A condition in which a relational operator tests the relationship between two values or expressions and returns a boolean result (true or false)  Relational / Equality operators: Allow comparison of the size, magnitude or equality of data items that are the same or compatible types.  For example:  less than ( < )…. 3 < 5 evaluates to true  bool isLessThan = 3 < 5;

RELATIONAL / EQUALITY OPERATORS OperatorMeaningTrue ExampleFalse Example <Less Than3 < 54 < 2 or 6 < 6 <=Less Than OR Equal To3 <= 4 or 3 <= 310 <= 5 >Greater Than8 > 79 > 10 or 4 > 4 >=Greater Than OR Equal To 5 >= 4 or 5 >= 55 > = 6 ==Equal To20 == 2010 == 11 !=Not Equal To10 != != 20 Evaluation of either a relational or equality operator always results to either true or false.

RELATIONAL / EQUALITY OPERATORS  Relational Operator Priority  (, >=) Are below the arithmetic operator  Equality Operator Priority  ( ==, !=) Are below the the relational operators

LOGICAL OPERATORS  Logical Operators ( !, &&, || ): Allow the combination of boolean values according to the rules of mathematical logic. Logical expressions evaluate to a boolean result (true or false)  Not (!)  Inverts the boolean value  true becomes false or false become true

LOGICAL OPERATORS  AND (&&)  Evaluates to true only if both values are true bool x; bool y; X&&Y== True&&True &&False &&TrueFalse &&False

LOGICAL OPERATORS  OR ( || )  Evaluates to false only if both values are false bool x; bool y; X||Y== True||True ||FalseTrue False||True False||False

OPERATOR PRECEDENCE  All operator precedence:

BOOLEAN, RELATIONAL, EQUALITY AND LOGICAL OPERATIORS  Example: bool flag1, flag2, flag3; int num1, num2; flag1 = (98 % 13 != 98 / 13) || (2 * 5 != 10); cout << "The truth value of variable flag1 is " << flag1 << endl; num1 = * 7; num2 = 10 + num1 % 3; flag2 = (num1 > num2) && (num2 < 12); cout << "The truth value of variable flag2 is " << flag2 << endl; flag3 = flag1 || !flag2; cout << "The truth value of variable flag3 is " << flag3 << endl;

SELECTION  MAKING CHOICES  One-Way (choose to do or not to do)  if  Two-Way (choose to do one or the other)  if – else  conditional operator  Multiple Selection(choose to do one of many)  nested if - else  switch

ONE-WAY SELECTION  SIMPLE  if ( RELATIONAL EXPRESSION(s) ) STATEMENT;  COMPOUND  if ( RELATIONAL EXPRESSION(s) ) { STATEMENT; STATEMENT(s); }

ONE WAY SELECTION  RULES 1.The statement(s) is/are executed if and only if the relational expression(s) evaluate(s) to true.

ONE WAY SELECTION  EXAMPLES: if (current_balance > 1000) interest = current_balance * 0.015; if (day == 7 && hours_worked > 40) { ot_pay = (hours_worked – 40) * pay_rate * 2; total_pay = 40 * pay_rate + ot_pay; }

ONE WAY SELECTION  EXAMPLE: int main() { bool isEven; int num; cout > num; cout 10) cout << num << " is greater than 10" << endl; isEven = (num % 2 == 0); if (isEven) cout << num << " is an EVEN number." << endl; if (!isEven) cout << num << " is an ODD number." << endl; system ("pause"); return 0; }

TWO WAY SELECTION  SIMPLE  if ( RELATIONAL EXPRESSION(s) ) Statement; else Statement;

TWO WAY SELECTION  COMPOUND  if ( RELATIONAL EXPRESSION(s) ) { Statement; Statement(s); } else { Statement; Statement(s); }

TWO 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 excuted if and only if the evaluation of the relational expression(s) is/are false.

TWO WAY SELECTION  EXAMPLES charemployee; stringstate; floatot_pay, pay_rate, gross_pay; floathours_worked, tax; Example 1: if (state == “CO”) tax = 0.065; else tax = 0.05;

TWO WAY SELECTION  EXAMPLES Example 2: if (employee == ‘E’ || employee == ‘S’) gross_pay = 40 * pay_rate; else { reg_pay = pay_rate * 40; ot_pay = (hours_worked – 10) * pay_rate * 1.5; gross_pay = reg_pay + ot_pay; }

CONDITIONAL OPERATOR  Can Accomplish Two Way Selection Using The Conditional Operator (?:)  expression1 ? expression2 : expression3  Example state == “CO” ? tax = : tax = 0.05;  Cannot Include Compound Statements