Control Structures

Control Structures

•A condition is represented by a logical (Boolean) expression that can be true or false

•Relational operators:

−Allow comparisons

−Require two operands (binary)

−Evaluate to true or false

Relational Operators and Simple Data Types

•You can use the relational operators with all three simple data types:

−8 < 15 evaluates to true

−6 != 6 evaluates to false

−2.5 > 5.8 evaluates to false

−5.9 <= 7.5 evaluates to true

−

Comparing Floating-Point Numbers for Equality

•Comparison of floating-point numbers for equality may not behave as you would expect

−Example:

•1.0 == 3.0/7.0 + 2.0/7.0 + 2.0/7.0 evaluates to false

•Why?  3.0/7.0 + 2.0/7.0 + 2.0/7.0 = 0.99999999999999989

•Solution: use a tolerance value

−Example: fabs(x – y) < 0.000001

Example

Comparing Characters

Relational Operators and the
string Type

•Relational operators can be applied to strings

•Strings are compared character by character, starting with the first character

•Comparison continues until either a mismatch is found or all characters are found equal

•If two strings of different lengths are compared and the comparison is equal to the last character of the shorter string

−The shorter string is less than the larger string

•Suppose we have the following declarations:

string str1 = "Hello";

string str2 = "Hi";

string str3 = "Air";

string str4 = "Bill";

string str4 = "Big";

Logical (Boolean) Operators and Logical Expressions 

Order of Precedence

•Relational and logical operators are evaluated from left to right

•The associativity is left to right

•Parentheses can override precedence

Example