Section 2 - More Basics

The char Data Type

• Data type of a single character

• Example

char letter;letter = 'C';

A type char character is encapsulated by single quotes ‘

Characters are encoded in the computer using a scheme where an integer represents a particular character

Examples ' ' encoded as 32 '+' encoded as 43

'A' encoded as 65 'Z' encoded as 90

'a' encoded as 97 'z' encoded as 122

This allows us to compare characters.

Character Operations

• Relational (aka comparison) operations are defined for characters types (as well as for other data types)

• The result is either true or false

– 'a' < 'b' is true– '4' > '3' is true– '6' <= '2' is false

Example - Read Characters

To read a character from the keyboard, use

char ch; cout << "Enter a character: ";cin >> ch;

Character Constants

Explicit (literal) characters within single quotes

'a','D','*'

Special characters - delineated by a backslash \

Two character sequences (escape codes)

Some important special escape codes

\t denotes a tab \n denotes a new line

\\ denotes a backslash \' denotes a single quote

\" denotes a double quote

To use, wrap up within single quotes

'\t' for the tab '\n' for the new line

Character Strings (aka Text Strings)

• Can store a series of characters (aka string) in consecutive memory locations:

"Hello“

• Stored with the null terminator, \0, at the end

• Comprises the characters between the " "

H e l l o \0

Literal String Constants

• A literal string constant is a sequence of zero or more characters enclosed in double quotes

– “Walk, don’t run"– “Bulgaria"– ""

• String is not a fundamental type- It is a C++ defined class

• To access a library use a preprocessor directive to add its definitions to your program file

#include <string>

string s = "Sharp";string t = “Dull";

Class string

Used to represent a sequence of characters as a single text string

Some definitions

string Name = “Ivan";

string DecimalPoint = ".";

string empty = "";

string copy = name;

string Question = '?'; // illegal

Class string

• Some string member functions

– size() determines number of characters in the stringstring Saying = "Rambling with Gambling";cout << Saying.size() << endl; // 22

– substr() determines a substring (Note first position has index 0)string Word = Saying.substr(9, 4); // with

– find() computes the position of a subsequenceint j = Saying.find("it"); // 10int k = Saying.find("its"); // ?

Class string

• Auxiliary operators

– + string concatenation – join strings togetherstring Part1 = "Me";string Part2 = " and ";string Part3 = "You";string All = Part1 + Part2 + Part3;

– += compound concatenation assignmentstring ThePlace = "Blagoevgrad";ThePlace += ", 2700";

Example

string fname = “Ivan";string lname = “Ivanov";string name = fname + lname;cout << name << endl;name = fname + " " + lname;cout << name << endl;

The output will beIvanIvanovIvan Ivanov

• Represents values that are true or false

• false is represented by 0, and true by 1

bool allDone = true;

bool finished = false;

• What happens here?bool b = true;int i = b;cout << b << endl;cout << i << endl;

The bool Data Type

Logical Expressions

Logical expressions have the one of two values - true or false

- A rectangle has three sides

- The instructor has a pleasant smile

Three key logical operations

And operations

Or operation

Not operation - negate

Type bool has two symbolic constants

truefalse

Logical (aka Boolean) operators

The And operator is &&

The Or operator is ||

The Not operator is !

Example logical expressions

bool P = true;

bool Q = false;

bool R = true;

bool S = (P && Q);

bool T = ((!Q) || R);

bool U = !(R && (!Q));

Write 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)

#include <iostream>using namespace std;

int main(){ int number; cout << "Enter an integer: "; cin >> number;

if (number % 2 == 0 && number % 3 == 0) cout << number << " is divisible by 2 and 3." << endl;

if (number % 2 == 0 || number % 3 == 0) cout << number << " is divisible by 2 or 3." << endl;

if ((number % 2 == 0 || number % 3 == 0) && !(number % 2 == 0 && number % 3 == 0)) cout << number << " divisible by 2 or 3, but not both." << endl;

return(0);}

How would you write this expression in C++

1 <= numberOfDaysInAMonth <= 31

Need to create a compound expression using Boolean operators

Relational Operators

Equality operators== test for equality

!= test for inequality

Examplesint i = 32;int k = 45;

bool q = (i == k); // false

bool r = (i != k); // true

Comments

Allow text commentary to be included in program

Importance

- Programs are read far more often than they are written

- Programs need to be understood so that they can be

maintained

C++ has two conventions for comments

// single line comment (preferred)

/* long comment */ (save for debugging)

Typical use

Describing the working of parts of a program

Enumerated Types

Allows the definition of programmer-defined types

enum Day {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY};

Once a type is defined, you can declare a variable of that type:

Day day;

The variable day can hold one of the values defined in the enumerated type. For example, the following statement assigns enumerated value MONDAY to variable day:

day = MONDAY;

Enumerated Types

As with any other type, you can declare and initialize a variable in one statement:

Day day = MONDAY;

Furthermore, C++ allows you to declare an enumerated type and variable in one statement. For example,

enum Day {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY} day = MONDAY;