Cs1123 11 pointers

Introduction to C++
(CS1123)
By
Dr. Muhammad Aleem,
Department of Computer Science,
Mohammad Ali Jinnah University, Islamabad
Fall 2013

History
• C evolved from two languages (BCPL and B)
• 1980: “C with Classes”
• 1985: C++ 1.0
• 1995: Draft standard
• Developed by Bjarne Stroustrup at Bell Labs
• Based on C, added Object-Oriented
Programming concepts (OOP) in C
• Similar program performance (compared to C)

C vs C++
• Advantages:
– 1. Faster development time (code reuse)
– 2. Creating / using new data types is easier
– 3. Easier memory management
– 4. Stricter syntax & type checking => less bugs
– 5. Easier to implement Data hiding
– 6. Object Oriented concepts

C++ Program Structure
//My first program in C++ First.cpp
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World!";
return 0;
}
Preprocessor
Directive (no ;)

IDE and Compilation Steps
C++
Preprocessor
First.cpp
C++ Compiler Linker First.exe
C++ Header
Files
Object code for
library function

Integrated Development Environments (IDEs)
• An IDE is a software application which provides a
comprehensive facility to programmers to Write /Edit
/Debug /Compile the code
• Main components:
–Source code editor
–Debugger
–Complier
–…

IDEs on Windows platform
• Turbo C++
• Microsoft Visual C++
• Dev C++

Input / Output Example
#include <iostream>
#include <string>
int main ( )
{
string name; //Name of student
cout<< “Enter you name";
cin>>name;
/* Now print hello , and students name */
cout<< “Hello “ << name;
return 0;
}

Comments
• Two types of comments
1. Single line comment //….
2. Multi-line (paragraph) comment /* */
• When compiler sees // it ignores all text after this on
same line
• When it sees /*, it scans for the text */ and ignores
any text between /* and */

Preprocessor Directives
• #include<iostream>
• # is a preprocessor directive.
• The preprocessor runs before the actual compiler and
prepares your program for compilation.
• Lines starting with # are directives to preprocessor to
perform certain tasks, e.g., “include” command
instructs the preprocessor to add the iostream library
in this program

Header files (functionality declarations)
(Turbo C++) (Visual C++)
• #include<iostream.h> or #include <iostream>
• #include<stdlib.h> or #include<stdlib>
• …

std:: Prefix
• std::cout<“Hello World”;
• std::cout<<Marks;
• std::cout<<“Hello ”<<name;
• Scope Resolution Operator ::
• std is a namespace, Namespaces ?
cout<<“Hello World”;
cout<<Marks;
cout<<“Hello ”<<name;

Namespaces
• Namespace pollution
– Occurs when building large systems from pieces
– Identical globally-visible names clash
– How many programs have a “print” function?
– Very difficult to fix

Namespaces
namespace Mine
{
const float pi = 3.1415925635;
}
void main(){
float x = 6 + Mine::pi;
cout<<x;
}

Multiple Namespaces
• Example…

Omitting std:: prefix
- using directive brings namespaces or its sub-items
into current scope
#include<iostream>
int main()
{
cout<<“Hello World!”<<endl;
cout<<“Bye!”;
return 0;
}

main( ) function
• Every C++ program start executing from main ( )
• A function is a construct that contains/encapsulates
statements in a block.
• Block starts from “{“ and ends with “}” brace
• Every statement in the block must end with a
semicolon ( ; )
• Examples…

cout and endl
• cout (console output) and the operator
• << referred to as the stream insertion operator
• << “Inserts values of data-items or string to
screen.”
• >> referred as stream extraction operator, extracts
value from stream and puts into “Variables”
• A string must be enclosed in quotation marks.
• endl stands for end line, sending ‘endl’ to the
console outputs a new line

Input and type
–cin>>name; reads characters until a
whitespace character is seen
–Whitespace characters:
• space,
• tab,
• newline {enter key}

Variables
- Variables are identifiers which represent
some unknown, or variable-value.
- A variable is named storage (some
memory address’s contents)
x = a + b;
Speed_Limit = 90;

Variable declaration
TYPE <Variable Name> ;
Examples:
int marks;
double Pi;
int suM;
char grade;
- NOTE: Variable names are case sensitive in C++ ??

Variable declaration
• C++ is case sensitive
–Example:
area
Area
AREA
ArEa
are all seen as different variables

Names
Valid Names
• Start with a letter
• Contains letters
• Contains digits
• Contains underscores
• Do not start names with underscores: _age
• Don’t use C++ Reserve Words

C++ Reserve Words
• auto break
• case char
• const continue
• default do
• double else
• enum extern
• float for
• goto if
int long
register return
short
signed
sizeof static
struct switch
typedef union
unsigned void
volatile while

Names
• Choose meaningful names
– Don’t use abbreviations and acronyms: mtbf, TLA,
myw, nbv
• Don't use overly long names
• Ok:
partial_sum
element_count
staple_partition
• Too long (valid but not good practice):
remaining_free_slots_in_the_symbol_table

Which are Legal Identifiers?
AREA
2D
Last Chance
x_yt3
Num-2
Grade***
area_under_the_curve
_Marks
#values
areaoFCirCLe
%done
return
Ifstatement

String input (Variables)
// Read first and second name
#include<iostream>
#include<string>
int main() {
string first;
string second;
cout << “Enter your first and second names:";
cin >> first >> second;
cout << "Hello “ << first << “ “ << second;
return 0;
}

Declaring Variables
• Before using you must declare the variables

Declaring Variables…
• When we declare a variable, what happens ?
– Memory allocation
• How much memory (data type)
– Memory associated with a name (variable name)
– The allocated space has a unique address
Marks
FE07
%$^%$%$*^%int Marks;

Using Variables: Initialization
• Variables may be given initial values, or
initialized, when declared. Examples:
int length = 7 ;
float diameter = 5.9 ;
char initial = ‘A’ ;
7
5.9
‘A’
length
diameter
initial

• Are the two occurrences of “a” in this expression the
same?
a = a + 1;
One on the left of the assignment refers to the location
of the variable (whose name is a, or address);
One on the right of the assignment refers to the value of
the variable (whose name is a);
• Two attributes of variables lvalue and rvalue
• The lvalue of a variable is its address
• The rvalue of a variable is its value
rvalue and lvalue

• Rule: On the left side of an assignment there
must be a lvalue or a variable (address of
memory location)
int i, j;
i = 7;
7 = i;
j * 4 = 7;
rvalue and lvalue

Data Types
Three basic PRE-DEFINED data types:
1. To store whole numbers
– int, long int, short int, unsigned int
2. To store real numbers
– float, double
3. Characters
– char

Types and literals
• Built-in types
– Boolean type
• bool
– Character types
• char
– Integer types
• int
–and short and
long
– Floating-point types
• double
–and float
• Standard-library types
– string
Literals
• Boolean: true, false
• Character literals
– 'a', 'x', '4', 'n', '$'
• Integer literals
– 0, 1, 123, -6,
• Floating point literals
– 1.2, 13.345, 0.3, -0.54,
• String literals
– "asdf”, “Helllo”, Pakistan”

Types
• C++ provides a set of types
– E.g. bool, char, int, double called “built-in types”
• C++ programmers can define new types
– Called “user-defined types”
• The C++ standard library provides a set of types
– E.g. string, vector, ..
– (for vector type  #include<vector> )

Declaration and initialization
int a = 7;
int b = 9;
char c = 'a';
double x = 1.2;
string s1 = "Hello, world";
string s2 = "1.2";
7
9
a
1.2
Hello, world
1.2

char type
• Reserves 8 bits or 1 byte of memory
• A char variable may represent:
– ASCII character 'A‘, 'a‘, '1‘, '4‘, '*‘
– signed integers 127 to -128 (Default)
– unsigned integer in range 255 to 0
Examples:
–char grade;
–unsigned char WeekNumber= 200;
–char cGradeA = 65;
–char cGradeAA = ‘A';

char type
• Example program…

Special characters
• Text string special characters (Escape Sequences)
– n = newline
– r = carriage return
– t = tab
– " = double quote
– ? = question
– = backslash
– ' = single quote
• Examples:
cout << "Hellot" << "I’m Bobn";
cout << "123nabc “;

Escape Sequence
• Example Program:

int type
• 16 bits (2 bytes) on Windows 16-bits
– int -32,768 to 32,767
– unsigned int 0 to 65,535
– Also on Turbo C++, 2 bytes for int
• 32 bits (4 bytes) on Win32 (Visual C++)
– int -2,147,483,648 to 2,147,483,647
– unsigned int 0 to 4,294,967,295

int type
• Examples:
int earth_diameter;
int seconds_in_week= 604800;
unsigned int Height = 100;
unsigned int Width = 50000;

int type (long and short)
• long int
–reserves 32 bits (4 bytes) of memory
–signed long -2,147,483,648 to 2,147,483,647
–unsigned long int 0 to 4,294,967,295
• short int
–reserves 16 bits (2 bytes) of memory
–signed short int -32,768 to 32,767
–unsigned short int 0 to 65,535

int (long and short)
• Examples:
long int light_speed=186000;
unsigned long int seconds= 604800;
short int Height = 30432;
unsigned short int Width = 50000;

Home Work-1
• Use Visual C++ on Windows and get information
for following data types:
– int
– short
– long int
– short int
– char
• Use ( cout << sizeof( intVar ); ) operator to get
this information, Example:…

Real Values
• float
– Reserves 32 bits (4 bytes) of memory
– + 1.180000x10
+38
, 7-digit precision
– Example: float radius= 33.4221;
• double
– Reserves 64 bits (8 bytes) of memory
– + 1.79000000000000x10
+308
, 15-digit precision
– Example: double Distance = 257.5434342;
• long double
– Reserves 80 bits (10 bytes) of memory , 18-digit precision
– Example: long double EarthMass = 25343427.53434233;

Home Work-2
• Use Visual C++ on Windows and get information
for following data types:
– float
– double
– long double
• Use ( cout << sizeof(floatVar); ) operator to get
this information, Example:…

bool Type
• Only 1 bit of memory required
– Generally, 1 byte because is reserved
• Literal values:
– true
– false
• Can be used in logical conditions:
– Examples:
bool RainToday=false;
bool passed;
passed = GetResult(80);

string type
• Special data type supports working with “strings”
#include <string>
string <variable_name> = “string literal”;
• string type variables in programs:
string firstName, lastName;
• Using with assignment operator:
firstName = “Mohammad";
lastName = “Ali";
• Display using cout
cout << firstName << " " << lastName;

Getting input in string with Spaces
string s1;
cin>> s1; //Spaces will not be input in s1
//Following statements read spaces in “string”
string s1;
getline(cin, s1); //Spaces will be input in s1

string type
• Find Errors in the example program…

Cs1123 11 pointers

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Cs1123 11 pointers