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CONTROL STRUCTURES (SELECTION)

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)

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CONTROL STRUCTURES (SELECTION)

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  1. CONTROL STRUCTURES(SELECTION)

  2. 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)

  3. 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

  4. 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

  5. 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;

  6. RELATIONAL / EQUALITY OPERATORS Evaluation of either a relational or equality operator always results to either true or false.

  7. RELATIONAL / EQUALITY OPERATORS • Relational Operator Priority • (<, <=, >, >=) Are below the arithmetic operator • Equality Operator Priority • ( ==, !=) Are below the the relational operators

  8. 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

  9. LOGICAL OPERATORS • AND (&&) • Evaluates to true only if both values are true bool x; bool y;

  10. LOGICAL OPERATORS • OR ( || ) • Evaluates to false only if both values are false bool x; bool y;

  11. OPERATOR PRECEDENCE • All operator precedence:

  12. 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 = 12 + 3 * 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;

  13. 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

  14. ONE-WAY SELECTION • SIMPLE • if ( RELATIONAL EXPRESSION(s) ) STATEMENT; • COMPOUND • if ( RELATIONAL EXPRESSION(s) ) { STATEMENT; STATEMENT; STATEMENT(s); }

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

  16. 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; }

  17. ONE WAY SELECTION • EXAMPLE: int main() {   bool isEven;   int num;   cout << "Enter an integer ";   cin >> num;   cout << endl;   if (num > 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; }

  18. TWO WAY SELECTION • SIMPLE • if ( RELATIONAL EXPRESSION(s) ) Statement; else Statement;

  19. TWO WAY SELECTION • COMPOUND • if ( RELATIONAL EXPRESSION(s) ) { Statement; Statement(s); } else { Statement; Statement(s); }

  20. 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.

  21. TWO WAY SELECTION • EXAMPLES char employee; string state; float ot_pay, pay_rate, gross_pay; float hours_worked, tax; Example 1: if (state == “CO”) tax = 0.065; else tax = 0.05;

  22. 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; }

  23. CONDITIONAL OPERATOR • Can Accomplish Two Way Selection Using The Conditional Operator (?:) • expression1 ? expression2 : expression3 • Example state == “CO” ? tax = 0.065 : tax = 0.05; • Cannot Include Compound Statements

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