Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X1 Chapter 3 Control Statements

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 2 Comparison Operators

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 3 Type bool expression: a combination of values, variables, operators and functions which, when evaluated, produce a value. examples: 2 + 2, pow(2, 2), ++i, k % 2 = = 0 Boolean expression (a.k.a. condition): an expression that results in a Boolean value, that is, true (1) or false (0). examples: 5 > 3, k % 2 = = 0, isupper(‘a’)  All conditions are expressions but not all expressions are conditions

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 4 Simple if Statements if (booleanExpression) { statement(s); } if (radius >= 0) { area = radius * radius * PI; cout << "The area for the circle of " << " radius " << radius << " is " << area; }

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 5 Examples Listing 3.1 gives a program that checks whether a number is even or odd. The program prompts the user to enter an integer (line 9) and displays “number is even” if it is even (lines 11-12) and “number is odd” if it is odd (lines 14-15). TestBoolean Run

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 6 Note

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 7 Caution Adding a semicolon at the end of an if clause is a common mistake. This mistake is hard to find, because it is not a compilation error or a runtime error, it is a logic error. This error often occurs when you use the next-line block style.

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 8 Boolean Operators Operator Name ! not && and || or

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 9 Truth Table for Operator &&

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 10 Truth Table for Operator ||

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 11 Examples Listing 3.3 gives a program that checks whether a number is divisible by 2 and 3, whether a number is divisible by 2 or 3, and whether a number is divisible by 2 or 3 but not both: TestBooleanOperators Run

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 12 Short-Circuit Operator When evaluating p1 && p2, C++ first evaluates p1 and then evaluates p2 if p1 is true; if p1 is false, it does not evaluate p2. When evaluating p1 || p2, C++ first evaluates p1 and then evaluates p2 if p1 is false; if p1 is true, it does not evaluate p2. Therefore, && is referred to as the conditional or short-circuit AND operator, and || is referred to as the conditional or short-circuit OR operator.

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 13 The if...else Statement if (booleanExpression) { statement(s)-for-the-true-case; } else { statement(s)-for-the-false-case; }

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 14 Examples Listing 3.4 presents a program that lets the user enter a year and checks whether it is a leap year. A year is a leap year if it is divisible by 4 but not by 100 or if it is divisible by 400. So you can use the following Boolean expression to check whether a year is a leap year: (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0) LeapYear Run

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 15 Nested if Statements if (i > k) { if (j > k) cout << "i and j are greater than k"; } else cout << "i is less than or equal to k";

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 16 Multiple Alternative if Statements

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 17 Note The else clause matches the most recent if clause in the same block.

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 18 Note, cont. Nothing is printed from the preceding statement. To force the else clause to match the first if clause, you must add a pair of braces: int i = 1; int j = 2; int k = 3; if (i > j) { if (i > k) cout << "A"; } else cout << "B"; This statement prints B.

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 19 TIP

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 20 CAUTION

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 21 Conditional Operator if (x > 0) y = 1 else y = -1; is equivalent to y = (x > 0) ? 1 : -1; (booleanExpression) ? expression1 : expression2 Ternary operator Binary operator Unary operator

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 22 Conditional Operator cout << ((num % 2 == 0) ? "num is even" : "num is odd");

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 23 Conditional Operator, cont. (booleanExp) ? exp1 : exp2

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 24 Operator Precedence How to evaluate * 4 > 5 * (4 + 3) – 1?

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 25 Operator Precedence F var++, var--  +, - (Unary plus and minus), ++var, --var F (type) Casting F ! (Not)  *, /, % (Multiplication, division, and remainder)  +, - (Binary addition and subtraction) , >= (Comparison)  ==, !=; (Equality) F && (Conditional AND) Short-circuit AND F || (Conditional OR) Short-circuit OR  =, +=, -=, *=, /=, %= (Assignment operator)

Liang, Introduction to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved X 26 Operator Precedence Simplified When in doubt, use parentheses version 1: if (ch >= ‘A’ && ch <= ‘Z’) cout << “UC”; version 2: if ((ch >= ‘A’) && (ch <= ‘Z’)) cout << “UC”;