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

cin and the Extraction Operator >>

<<cin 

•The syntax of an input statement using cin and the extraction operator >> is:

cin >> variable 1>>variable2;

 

•The extraction operator >> is binary

−Left-side operand is an input stream variable

•Example: cin

−Right-side operand is a variable

•No difference between a single cin with multiple variables and multiple cin statements with one variable

•When scanning, >> skips all whitespace

−Blanks and certain nonprintable characters

>> distinguishes between character 2 and number 2 by the right-side operand of >>

−If type char or int (or double), the 2 is treated as a character or as a number 2

I/O Streams and Standard I/O Devices

I/O: sequence of bytes (stream of 

bytes) from source to destination

Bytes are usually characters, unless program requires other types of information

Stream: sequence of characters from 

source to destination

Input stream: sequence of characters 

from an input device to the computer

Output stream: sequence of 

characters 

from the computer to an output 

device

•Use iostream header file to 

extract (receive) data from keyboard 

and send output to the screen

−Contains definitions of two data 

types:

•istream - input stream

•ostream - output stream

−Has two variables:

•cin - stands for common input

•cout - stands for common output

•To use cin and cout, the 

preprocessor directive  

#include <iostream> 

must be used

•Variable declaration is 

similar to:

−istream cin;

−ostream cout;

•Input stream variables: type 

istream

•Output stream variables: 

type ostream

chapter 3 part 3 :Arithmetic Operator and Operator Precedence

Arithmetic Operators  and  

     

     Operator Precedence

C++ arithmetic operators:

−+ addition

−- subtraction

−* multiplication

−/ division

−% modulus operator

+, -, *, and / can be used with integral and floating-point data types

Operators can be unary or binary

Order of Precedence

All operations inside of () are 

evaluated first

*, /, and % are at the same level of 

precedence and are evaluated 

next

+ and – have the same level of 

precedence and are evaluated last

When operators are on the same 

level

−Performed from left to right 

(associativity)

3 * 7 - 6 + 2 * 5 / 4 + 6 

means

(((3 * 7) – 6) + ((2 * 5) / 

4 

)) + 6

Expressions

•If all operands are integers

−Expression is called an integral expression

•Yields an integral result

•Example: 2 + 3 * 5

•If all operands are floating-point

−Expression is called a floating-point expression

•Yields a floating-point result

•Example: 12.8 * 17.5 - 34.50

Mixed Expressions

•Mixed expression:

−Has operands of different data types

−Contains integers and floating-point

•Examples of mixed expressions:

2 + 3.5

6  /  4 + 3.9

chapter 3 part2

int Data Type

•Examples:

-6728

0

78

+763

•Positive integers do not need a + sign

•No commas are used within an integer

−Commas are used for separating items in a list

bool Data Type

•bool type

Two values: true and false

Manipulate logical (Boolean) 

expressions

true and false are called logical 

values

bool, true, and false are 

reserved words

char Data Type

The smallest integral data type

Used for characters: letters, digits, 

and special symbols

Each character is enclosed in 

single quotes

'A', 'a', '0', '*', '+', '$', 

'&'

A blank space is a character and 

is written ' ', with a space left 

between the single quotes