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
H
e
l
l
o
\0
• Comprises the characters between the " "
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 string
string 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 subsequence
int j = Saying.find("it");
// 10
int k = Saying.find("its");
// ?
Class string
• Auxiliary operators
– + string concatenation – join strings together
string Part1 = "Me";
string Part2 = " and ";
string Part3 = "You";
string All = Part1 + Part2 + Part3;
– += compound concatenation assignment
string 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 be
IvanIvanov
Ivan Ivanov
The bool Data Type
• 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;
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
true
false
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
Examples
int 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;