Post on 25-Feb-2023
What is C++?
C++ is a programming language.
A computer program performs a specific task, and
may interact with the user and the computer
hardware.
Human work model:
Computer work model:
What is C++? The most popular programming languages:
Basic (Beginner All-purpose Symbolic Instructional Code)
C++ (an object-oriented language, based on C)
Fortran (FORmula TRANslation)
Java
Pascal (named for Blaise Pascal)
Visual Basic (Basic-like visual language developed by Microsoft)
C (developed by the designer of the B language)
The most common versions of C++:
Microsoft VC++
Eclipse
g++ (for Unix machines)
Why C++?
Bad News:
C++ is not easy to learn
Good News:
Lots of good-paying jobs for programmers because C++ is not easy to learn!
Java uses C++ syntax, it is easy to learn Java if you know C++.
Though C++ is not the easiest language (Basic and Pascal are easier), it is not the hardest either (Prolog and Assembly languages are really difficult!)
Who Uses C++?
Computer makers such as Sun, SGI, IBM, and HP
Airport
Computer chip manufacturers
like Motorola & Intel
Software companies
Banks
Government
Hospital Authority
Telecommunications
Universities
Most Important Feature of C++
Most important feature of C++: its strong and efficient support of both Structured Programming and Object-Oriented Programming.
C++ runs on:
PC
Macintosh
Unix workstations (also, Unix versions of C++ are free!)
supercomputers
Computer Software Relationships
User
Interface
Basic Input and Output Services (BIOS)
• needed for a computer to boot up
User Interface Operating System
User Interface Application Programs
Computer Hardware
Introduction to C++
C is a programming language developed in the 1970's alongside the UNIX operating system.
C provides a comprehensive set of features for handling a wide variety of applications, such as systems development and scientific computation.
C++ is an “extension” of the C language, in that most C programs are also C++ programs.
C++, as opposed to C, supports “object-oriented programming.”
General form of a C++ program
// Program description
#include directives
int main()
{
constant declarations
variable declarations
executable statements
return 0;
}
C++ keywords
Keywords appear in blue in Visual C++.
Each keyword has a predefined purpose in the language.
Do not use keywords as variable and constant names!!
Common keywords:
bool, break, case, char, const,
continue, do, default, double, else,
extern, false, float, for, if, int, long,
namespace, return, short, static, struct,
switch, typedef, true, unsigned, void,
while
Example – adding 2 numbers
Peter: Hey Frank, I just learned how to add two numbers together.
Frank: Cool!
Peter : Give me the first number.
Frank: 2.
Peter : Ok, and give me the second number.
Frank: 5.
Peter : Ok, here's the answer: 2 + 5 = 7.
Frank: Wow! You are amazing!
after Frank says “2”, Peter has to keep this number in his mind.
2 5 7 First number: Second number: Sum:
after Frank says “5”, Peter also needs to keep this number in his mind.
The Corresponding C++ Program
#include <iostream>
using namespace std;
int main()
{
int first, second, sum;
cout << "Peter: Hey Frank, I just learned how to add”
<< “ two numbers together."<< endl;
cout << "Frank: Cool!" <<endl;
cout << "Peter: Give me the first number."<< endl;
cout << "Frank: ";
cin >> first;
cout << "Peter: Give me the second number."<< endl;
cout << "Frank: ";
cin >> second;
sum = first + second;
cout << "Peter: OK, here is the answer:";
cout << sum << endl;
cout << "Frank: Wow! You are amazing!" << endl;
return 0;
}
#include <iostream>
using namespace std;
int main()
{
int number_of_pods, peas_per_pod, total_peas;
cout << "Press return after entering a number.\n";
cout << "Enter the number of pods:\n";
cin >> number_of_pods;
cout << "Enter the number of peas in a pod:\n";
cin >> peas_per_pod;
total_peas = number_of_pods * peas_per_pod;
Demo Example
cout << "If you have ";
cout << number_of_pods;
cout << " pea pots\n";
cout << "and ";
cout << peas_per_pod;
cout << " pea in each pod, then \n";
cout << "you have ";
cout << total_peas;
cout << " peas in all the pods.\n";
return 0;
}
Demo Example
Identifiers appear in black in Visual C++.
An identifier is a name for a variable, constant, function, etc.
It consists of a letter followed by any sequence of letters, digits, and underscores.
Examples of valid identifiers: First_name, age, y2000, y2k
Examples of invalid identifiers: 2000y
Identifiers cannot have special characters in them. For example: X=Y, J-20, ~Ricky,*Michael are invalid identifiers.
Identifiers are case-sensitive. For example: Hello, hello, WHOAMI, WhoAmI, whoami are unique identifiers.
C++ identifiers
C++ comments
Comments appear in green in Visual C++.
Comments are explanatory notes; they are ignored by the compiler.
There are two ways to include comments in a program:
// A double slash marks the start of a
//single line comment.
/* A slash followed by an asterisk marks
the start of a multiple line comment. It
ends with an asterisk followed by a
slash. */
C++ compiler directives
Compiler directives appear in blue in Visual C++.
The #include directive tells the compiler to include
some already existing C++ code in your program.
The included file is then linked with the program.
There are two forms of #include statements:
#include <iostream> //for pre-defined
files
#include "my_lib.h" //for user-defined
files
Programming Style
C++ is a free-format language, which means that:
Extra blanks (spaces) or tabs before or after identifiers/operators are ignored.
Blank lines are ignored by the compiler just like comments.
Code can be indented in any way.
There can be more than one statement on a single line.
A single statement can continue over several lines.
In order to improve the readability of your program, use the following conventions:
Start the program with a header that tells what the program does.
Use meaningful variable names.
Document each variable declaration with a comment telling what the variable is used for.
Place each executable statement on a single line.
A segment of code is a sequence of executable statements that belong together.
Use blank lines to separate different segments of code.
Document each segment of code with a comment telling what the segment does.
Programming Style (cont. )
What makes a bad program?
Writing Code without detailed analysis
and design
Repeating trial and error without
understanding the problem
Debugging the program line by line,
statement by statement
Writing tricky and dirty programs
C++ Data Type
A type defines a set of values and a set of
operations that can be applied on those values.
The set of values for each type is known as the
domain for the type.
C++ contains 5 standard types:
void int char float bool
Standard
Data Types
void
The void type has no values and no operations. In
other words, both the set of values and the set of
operations are empty. Although this might seem
unusual, we will see later that it is a very useful data
type.
Integer
An integer type is a number without a fractional
part. It is also known as an integral number. C++ supports three different sizes of the integer data type: short int, int and long int.
sizeof(short int)<= sizeof(int)<= sizeof(long int)
Short int
int
long int
Floating Point
A floating-point type is a number with a fractional
part, such as 43.32. The C++ language supports
three different sizes of floating-point: float, double
and long double.
sizeof(float)<= sizeof(double)<= sizeof(long double)
float
double
long double
Floating Point
type Byte size Number of Bits
float 4 32
double 8 64
long double 10 80
Although the physical size of floating-point types is
machine dependent, many computers support the
sizes shown below.
Declarations
Constants and variables must be declared before they can be used.
A constant declaration specifies the type, the name and the value of the constant.
A variable declaration specifies the type, the name and possibly the initial value of the variable.
When you declare a constant or a variable, the compiler: Reserves a memory location in which to store the value of the
constant or variable.
Associates the name of the constant or variable with the memory location. (You will use this name for referring to the constant or variable.)
Constant declarations
Constants are used to store values that never change during the program execution.
Using constants makes programs more readable and maintainable.
Syntax: const <type> <identifier> = <expression>;
Examples: const double UK2USD = 1.6;
//Exchange rate of £ to $
const double fee = 16000;
//Tuition fee
Variables are used to store values that can be changed
during the program execution.
A variable is best thought of as a container for a value.
3445 y -3.14
Syntax: < type > < identifier >;
< type > < identifier > = < expression >;
Examples: int sum;
int total = 3445;
char answer = 'y';
double temperature = -3.14;
Variable declarations
A variable has a type and it can contain only values of that type. For example, a variable of the type int can
only hold integer values.
Variables are not automatically initialized. For example,
after declaration int sum;
the value of the variable sum can be anything (garbage).
Thus, it is good practice to initialize variables when they
are declared.
Once a value has been placed in a variable it stays
there until the program deliberately alters it.
Variable declarations
Character data
A variable or a constant of char type can hold an ASCII
character (see Appendix A of the textbook).
When initializing a constant or a variable of char type, or
when changing the value of a variable of char type, the
value is enclosed in single quotation marks.
Examples:
const char star = '*';
char letter, one = '1';
Rules for Division
C++ treats integers differently from decimal numbers.
100 is an int type.
100.0 , 100.0000, and 100. are double type.
The general rule for division of int and double types is:
double/double -> double (normal)
double/int -> double (normal)
int/double -> double (normal)
int/int -> int (note: the decimal part is discarded)
Rules for Division
Examples:
220. / 100.0 double/double -> double result is 2.2
220. / 100 double/int -> double result is 2.2
220 / 100.0 int/double -> double result is 2.2
220 / 100 int/int -> int result is 2
Summary: division is normal unless both the numerator and denominator are int, then the result is an int (the decimal part is
discarded).
Assignment Conversions
A decimal number assigned to an int type variable
is truncated.
An integer assigned to a double type variable is
converted to a decimal number.
Example 1:
double yy = 2.7;
int i = 15;
int j = 10;
i = yy; // i is now 2
yy = j; // yy is now 10.0
Assignment Conversions
Example 2:
int m, n;
double xx;
m = 7;
n = 2.5;
xx = m / n;
n = xx + m / 2;
// What is the value of n?
Assignment Conversions
Example 2:
int m, n;
double xx;
m = 7;
n = 2.5; // 2.5 converted to 2 and assigned to n
xx = m/n; // 7/2=3 converted to 3.0 and assigned to xx
n = xx+m/2;
// m/2=3 : integer division
// xx+m/2 : double addition because xx is double
// convert result of m/2 to double (i.e. 3.0)
// xx+m/2=6.0
// convert result of xx+m/2 to int (i.e. 6)
// because n is int
Forcing a Type Change
You can change the type of an expression with a cast
operation.
Syntax: variable1 = type(variable2);
variable1 = type(expression);
Example: int x=1, y=2;
double result1 = x/y; // result1 is 0.0
double result2 = double(x)/y; // result2 is 0.5
double result3 = x/double(y); // result3 is 0.5
double result4 = double(x)/double(y);// result4 is 0.5
double result5 = double(x/y); // result5 is 0.0
int cents = int(result4*100); // cents is 50
Standard Input/Output
cin - the standard input stream
Input operator “>>”
Extracts data from input “stream” (the keyboard by default).
Skips over white spaces.
Extracts only characters of the right form and performs
automatic conversion to the type specified.
Standard Input/Output
cout - the standard output stream
Output operator “<<”
Inserts data into the output “stream” (the screen by default).
Example:
int id, score;
cout << "Enter student ID and score: ";
cin >> id >> score;
cout << "Student ID: " << id << " score: "
<< score << endl;
Standard Input/Output
Some special output characters:
\a bell
\t tab
\n new line
\' single quote
\" double quote
Format Manipulation
#include <iomanip>
setw(int size)
Specifies the number of characters to use in displaying the next value,
which is right-justified.
Ex: cout << setw(5) << 12;
//output 3 spaces and then 12
setprecision(int digit)
Specifies the number of significant digits for all subsequent output.
cout << fixed << setprecision(2);
the precision is: two digits after the decimal point.
Fixed: uses fixed-point notation in the float field