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Decisions

Decisions. Given hours worked and pay rate, calculate total pay What if you work overtime? How do you indicate if your work overtime? How about double overtime?. < less than <= less than or equal to > greater than >= greater than or equal to == equals != not equal to.

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Decisions

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  1. Decisions • Given hours worked and pay rate, calculate total pay • What if you work overtime? • How do you indicate if your work overtime? • How about double overtime? COSC175-Selection

  2. <less than <= less than or equal to > greater than >= greater than or equal to == equals != not equal to Relational Operators COSC175-Selection

  3. Examples • 10 > 2 • 'a' < 'c' Why is this true? • x != y • temp > humidity • num == 35 • initial != ‘Q’ COSC175-Selection

  4. Logicals: AND && OR || NOT ! COSC175-Selection

  5. Examples 1. if ((sex == 'F') && (city_code == 18) && (gpa >= 3.7)) cout << "Merit Award" << endl; 2. if ((zip == "48002") || (zip == "48003") || (zip == "48004")) cout << "LOCAL“ << endl; COSC175-Selection

  6. “Short-Circuit” Evaluation • Process in which the computer evaluates a logical expression from left to right and stops as soon as the value of the expression is known • one True in || -> True • one False in && -> False Example: int age; int height; age = 25; height = 70; • ((age > 50) && (height > 60)) 2. ((height > 60) || (age > 40))

  7. Selection/Decision • Test – true or false • One operation performed if true • One operation performed if false • Keywords • if, else COSC175-Selection

  8. if Syntax if ( Expression ) statement NOTE: statement can be a single statement, a null statement, or a compound statement. COSC175-Selection

  9. if statement is a selection of whether or not to execute a statement (which can be a single statement or an entire block) TRUE expression FALSE statement COSC175-Selection

  10. Examples • if (taxCode == ‘T’ ) price = price + taxRate*Price; 2. if (num < 0 ) { // compound statement cout << "Negative" << endl; numNegs = numNegs + 1; } 3. if (age < 21 ) cout << "Under Age" COSC175-Selection

  11. if-else Syntax if ( Expression ) StatementA else StatementB NOTE: StatementA and StatementB each can be a single statement a null statement, or a compound statement. COSC175-Selection

  12. if..else provides two-way selection between executing one of 2 clauses (the if clause or the else clause) TRUE FALSE expression if clause else clause COSC175-Selection

  13. int carDoors, driverAge; float premium, monthlyPayment; . . . if ( (carDoors == 4 ) && (driverAge > 24) ) { premium = 650.00 cout << "LOW RISK “ << endl; } else { premium = 1200.00 cout << “ HIGH RISK ” << endl; } monthlyPayment = premium / 12.0 + 5.00; COSC175-Selection

  14. Example Convert temperature from fahrenheit to celsius or from celsius to fahrenheit based on C or F COSC175-Selection

  15. code int main() { float temp; float newTemp; char units; cout << " Enter temperature and C or F" cin >> temp >> units; if (units == 'F') { newTemp = (5 * (temp – 32) )/9; cout << temp<< "Degrees F = " <<newTemp<<" Degrees C“; } else { newTemp = ((9 * temp)/5) + 32; cout << "Degrees C = " << newTemp << " Degrees F“ << endl; } } // end main COSC175-Selection

  16. Exercises: • Write the statements that allow you to input a number and prints whether it is positive or negative. • Write the statements necessary to input the price of apples and the price of oranges. Then print either "THE APPLES COST MORE" or "THE ORANGES COST MORE. How would you handle the situation where the cost was the same? • Write the statements that allow you to input a number and prints whether it is odd or even. COSC175-Selection

  17. Nested selection - Example if (hrsWorked <= 40 ) totPay = hrsWorked * payRate; else { regPay = 40 * payRate; if (hrsWorked <= 60) { otPay = (hrsWorked – 40) * (1.5 * payRate); totPay = regPay + otPay; } else { otPay = 20 * (1.5 * payRate); doubleOtPay = (hrsWorked – 60) * (2 * payRate); grossPay = regPay + otPay + doubleOtPay; } } COSC175-Selection

  18. if (x > 0) cout << “Positive” << endl; else if (x < 0) cout << “Negative” << endl; else cout << “Zero” << endl; if (x > 0) cout << “Positive” << endl; else if (x < 0) cout << “Negative” << endl; else cout << “Zero” << endl; Writing a nested if statement as a Multiple-Alternative Decision COSC175-Selection

  19. cin >> testGrade if (testGrade >= 90) letterGrade = ‘A‘; else if (testGrade >= 80) && testGrade < 90 letterGrade = 'B‘; else if (testGrade >= 70) && testGrade < 80 letterGrade = 'C‘; else if (testGrade >= 60) && testGrade < 70 letterGrade = 'D‘; else if testGrade < 60 letterGrade = 'F‘; • Why is italicized code not necessary? COSC175-Selection

  20. cin >> testGrade if (testGrade >= 90) letterGrade = 'A‘; else if (testGrade >= 80 ) letterGrade = 'B‘; else if (testGrade >= 70 ) letterGrade = 'C‘; else if (testGrade >= 60 ) letterGrade = 'D‘; else letterGrade = 'F‘; COSC175-Selection

  21. Nested if Statements if ( Expression1 ) Statement1 else if ( Expression2 ) Statement2 . . . else if ( ExpressionN ) StatementN else Statement N+1 EXACTLY 1 of these statements will be executed. COSC175-Selection

  22. Multi-way Branching if ( creditsEarned >= 90 ) cout << “SENIOR STATUS “; else if ( creditsEarned >= 60 ) cout <<“JUNIOR STATUS “; else if ( creditsEarned >= 30 ) cout << “SOPHOMORE STATUS “; else cout << “FRESHMAN STATUS “; COSC175-Selection

  23. if (age < 16) charge = 7; if ((age >= 16) && (age < 65)) charge = 10; if (age >= 65) charge = 5; if (age < 16 ) charge = 7; else if ((age >= 16) && (age < 65)) charge = 10; else if (age >= 65 ) charge = 5; Use nested logic rather than straight thru logic COSC175-Selection

  24. Testing Selection Control Structures • to test a program with branches, use enough data sets so that every branch is executed at least once • this is called minimum complete coverage COSC175-Selection

  25. switch • Use for multiple tests of one variable switch (selector) { case label1: statement 1 case label2: statement 2 .. case label n: statement n default: statement e } COSC175-Selection

  26. Example cin >> menuOpt; switch (menuOpt) { case 1: cout << "Beginners“; break; case 2: cout << "Advanced Beginner“; break; case 3: cout << "Intermediate“; break; default: cout << "Invalid Option“ } //END CASE COSC175-Selection

  27. Example cin >> menuOpt; switch (menuOpt) { case 1: case 2: cout << “Buckle my shoe“; break; case 3: case 4: cout << “Shut the door“; break; case 5: case 6: cout << “Pick up stickse“; break; default: cout << "Invalid Option“ } //END CASE COSC175-Selection

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