Transcript Introduction To C++

Introduction to programming
using C++
Dr. Mohamed Khafagy
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.”

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:
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 (Ada,
Prolog and Assembly languages are really difficult!)
Who Uses C++?

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Computer makers such as Sun, SGI, IBM, and HP
Airport
Computer chip manufacturers
like Motorola & Intel
Software companies
Banks
Hong Kong Government
Hospital Authority
Telecommunications
Universities
What Can We Do
By the End of the Course?
Program the computer in applications
such as
the following:
 Program a simple calculator
 Program simple computer games
 Program a small inventory system for a small
company
Programming
and Problem Solving

Algorithm
◦ A sequence of precise instructions which
leads to a solution

Program
◦ An algorithm expressed in a language the
computer can understand
Software Life Cycle
1. Analysis and specification of the task
(problem definition)
2. Design of the software
(object and algorithm design)
3. Implementation (coding)
4. Maintenance and evolution of the system
5. Obsolescence
Questions
 Can you…
◦ Describe the first step to take when creating a
program?
◦ List the two main phases of the program design
process?
◦ Explain the importance of the problem-solving phase?
◦ List the steps in the software life cycle?
Specification of a problem
A precise statement/description of the
problem.
 It involves describing the input, the
expected output, and the relationship
between the input and output.
 This is often done through preconditions
and postconditions.

Design
Formulation of a method, that is, of a sequence
of steps, to solve the problem.
 The design “language” can be pseudo-code,
flowcharts, natural language, any combinations
of those, etc.
 A design so expressed is called an algorithm(s).
 A good design approach is a top-down design
where the problem is decomposed into smaller,
simpler pieces, where each piece is designed
into a module.

Implementation
Development of actual C++ code that will
carry out the design and solve the
problem.
 The design and implementation of data
structures, abstract data types, and classes,
are often a major part of design
implementation.

Analysis of the Solution
Estimation of how much time and memory an
algorithm takes.
The purpose is twofold:
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◦
◦
to get a ballpark figure of the speed and memory
requirements to see if they meet the target
to compare competing designs and thus choose
the best before any further investment in the
application (implementation, testing, etc.)
Testing and Debugging
Testing a program for syntactical correctness (no
compiler errors)
Testing a program for semantic correctness, that is,
checking if the program gives the correct output.
This is done by
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
◦
◦
◦
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having sample input data and corresponding, known output
data
running the programs against the sample input
comparing the program output to the known output
in case there is no match, modify the code to achieve a
perfect match.
One important tip for thorough testing: Fully exercise
the code, that is, make sure each line of your code is
executed.
Maintenance and Evolution of a
System

Ongoing, on-the-job modifications and
updates of the programs.
1.4
Testing and Debugging

Bug
◦ A mistake in a program

Debugging
◦ Eliminating mistakes in programs
◦ Term used when a moth caused a failed relay
on the Harvard Mark 1 computer. Grace
Hopper
and other programmers taped the moth in
logbook
stating:
“First actual case of a bug being found.”
Program Errors

Syntax errors
◦ Violation of the grammar rules of the language
◦ Discovered by the compiler
 Error messages may not always show correct location of
errors

Run-time errors
◦ Error conditions detected by the computer at runtime

Logic errors
◦ Errors in the program’s algorithm
◦ Most difficult to diagnose
◦ Computer does not recognize an error
Questions

Can you…
◦ Describe the three kinds of program errors?
◦ Tell what kind of errors the compiler catches?
◦ What kind of error is produced if you forget
a
punctuation symbol such as a semi-colon?
◦ Tell what type of error is produced when a
program
runs but produces incorrect results?
Programming as a Problem Solving
Process

Define and analyze the problem.
◦ What is the input & output?
◦ What other information is necessary?

Develop an algorithm.
◦ What steps must be done?
Implement a program.
 Compile, test, and debug the program.
 Document and maintain the program.
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Algorithms
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Sequential steps for solving a problem or task

Language independent

Written in plain English
Allows programmers to concentrate on the
solution
 without worrying about the implementation
details

Cake Algorithm
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Stir into a large mixing bowl
2 eggs
4cups of water
Cake mix
Once all the lumps are gone
Preheat oven to 400 degrees
Place cake mix in a 4X7 greased cake pan
Bake for 35 minutes
Cool for 15 minutes and serve
Simple Sort Algorithm

1.Get a list of unsorted numbers
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2.Repeat steps 3 through 6 until the unsorted list is empty
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3.Compare the unsorted numbers
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4.Select the smallest unsorted number
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5.Move this number to the sorted list
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6.Remove the selected smallest number from the unsorted
list

7.Stop

Simple Sort Algorithm
There are two commonly used tools to
help to document program logic (the
algorithm).
 These are flowcharts and
Pseudocode.
 in flowcharts are shown below:

With flowcharting, essential steps of an
algorithm are shown using the shapes
above. The flow of data between steps is
indicated by arrows, or flowlines.
 For example, a flowchart (and equivalent
 Pseudocode) to compute the interest on
a loan is shown below:

Example

Problem Statement
◦ Given a collection of nickels (US 5-cent coins) and pennies (US 1cent coins), find the equivalent number of Hong Kong dollars

Problem Analysis
◦ Input:
 nickels (integer) - number of US nickels
 pennies (integer) - number of US pennies
◦ Output:
 dollars (integer) - number of HK dollar coins to return

Example: Initial Algorithm
1. Read in the numbers of nickels and pennies.
2. Compute the total value in US dollars.
3. Compute the corresponding total value in HK
dollars.
4. Find the number of HK dollar coins
5. Display the number of HK dollar coins
Example: Refined Algorithm
1.
Read in the number of nickels and pennies and
US2HK .
2. Compute the total value in US dollars.
2.1 total_USD = (5 * nickel + penny)/100
3. Compute the corresponding total in HK dollars.
3.1. total_HKD = total_USD * US2HK
4. Find the number of HK dollar coins.
4.1. total_HK_cent = total_HKD * 100
4.2. dollar = total_HK_cent / 100
5. Display the number of HK dollar.
Flowchart
Pseudocode
Read NAME, BALANCE, RATE
 Compute INTEREST as BALANCE x
RATE
 Write (Display) NAME and INTEREST

Read X,Y, Z
 Compute Sum (S) as X + Y + Z
 Compute Average (A) as S / 3
 Compute Product (P) as X x Y x Z
 Write (Display) the Sum, Average and
Product
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The example below shows the flowchart
for a program that reads two numbers
and displays the numbers read in
decreasing order
Read A, B
 If A is less than B
 BIG = B
 SMALL = A
 else
 BIG = A
 SMALL = B
 Write (Display) BIG, SMALL

General form of a C++ program
// Program description
#include directives
int main(){
constant declarations
variable declarations
executable statements
return 0;
}
Declarations
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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:
1. Reserves a memory location in which to store the
value of the constant or variable.
2. Associates the name of the constant or variable with
the memory location. (You will use this name for
referring to the constant or variable.)
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For more on declarations, see www.courseware.ust.hk and choose
English--> C++ --> Declarations.
Variable declarations
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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
Syntax:
< type >< identifier >;
< type >< identifier >=< expression >;
Examples:
int sum;
int total = 3445;
char answer = 'y';
double temperature = -3.14;
Variable declarations
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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;
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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.
Character data

A variable or a constant of char type can hold
an ASCII character

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';
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 US2HK = 7.8;
//Exchange rate of US$ to HK$
const double HK2TW = 3.98;
//Exchange rate of HK$ to TW$
const double US2TW = US2HK * HK2TW;
//Exchange rate of US$ to TW$
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:
Standard
Data Types
void
int
char
float
bool
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
Integer
The type also defines the size of the field in which data can be stored. In C++,
even though the size is machine dependent, most PCs use the integer sizes
shown below.
Type
Sign
Byte N. of Min Value Max Value
Size Bits
short int Signed
2
unsigned
int
long int
16
-32768
0
32767
65535
Signed
4
unsigned
32
-2,147,483,648
2,147,483,647
Signed
4
unsigned
32
0
-2,147,483,648
4,294,967,295
2,147,483,647
4,294,967,295
0
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
Although the physical size of floating-point types is machine dependent,
many computers support the sizes shown below.
type
Byte size
Number of Bits
float
4
32
double
8
64
10
80
long double
More Data Types

bool
◦ 8 bits
◦ either trueor false

string
◦ Class type
◦ Defined in double quotes
◦ Must include the <string> library
Identifier Names (i.e., Symbols)
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Variables, functions, structures, classes, etc.
Prules
◦ Are case sensitive
◦ Must begin with a letter, which includes an
nderscore (_)
◦ Subsequent characters may be letters, digits, and
underscores
◦ Cannot be a keyword
◦ May only be defined once in a scope
◦ Should avoid library names
◦ Must be declared before use
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!!
 The complete list of keywords is on page 673 of the textbook.
 We shall cover the following keywords in this class:

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
Variables
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Name a region of memory where data is stored
Must be defined before use: includes data type
and name
Names are case sensitive
Examples (definition and initialization)
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int dollars;
int quarters, dimes, nickels, pennies;
int money = 217;
double x, pi = 3.14159;
char begin = 'A', end = 'Z', newLine = '\n‘;
Assignment
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Literal Values
someInt= 27;
someDub= 33.33;
Expressions
someInt= 27+ 23;
someDub= 5.55 * 1.0;
Values of other Variables
someInt= someOtherInt;
someDub= someOtherDub;
someInt= someInt2 + someInt3;
someDub= someDub2 / someDub3;
Multiple Assignment and Combined
Assignment

=is an operator that can be used > 1 time
in an expression:
x = y = z = 5;
 Value of =is the value that is assigned
 Associates right to left:
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x = (y = (z = 5));
Comments
◦ Single line Comments// ‐single line comment
// Name: Brad Rippe
 // File:Assignment23.cpp
 // Date:1/21/07

◦ Multiple line Comments/* … */
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/*
Name: Brad Rippe
File:Assignment23.cpp
Date:1/21/07
*/
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:
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◦
◦
◦
◦
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
220. / 100
220 / 100.0
220 / 100
double/double -> double result
double/int -> double
int/double -> double
int/int -> int
is 2.2
result is 2.2
result is 2.2
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
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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:
\t
\n
tab
new line
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
// Demonstrate the features of output format manipulators
// Input: cost of lunch, number of people attending lunch
// Output: lunch cost per person
#include <iomanip> // Use IO manipulators
#include <iostream>
using namespace std;
int main() {
double cost_of_lunch, cost_per_person;
int number_of_people;
cout << "Press return after entering a number.\n";
cout << "Enter the cost of lunch:\n";
cin >> cost_of_lunch;
cout << "Enter the number of people attending lunch:\n";
cin >> number_of_people;
cost_per_person = cost_of_lunch / number_of_people;
//cout << setiosflags(ios::fixed) << setprecision(2);
cout << "If the lunch cost $";
cout << cost_of_lunch;
cout << ", and you have " << number_of_people
<< " persons attending, then \n";
cout << "the cost per person is $"
<< cost_per_person << ".\n";
/*
cout << "the cost per person is $";
cout << setprecision(4) << cost_per_person <<
".\n";
*/
return 0;
}
Output of example program:
Press return after entering a number.
Enter the cost of lunch:
800.75
Enter the number of people attending lunch:
9
If the lunch cost $800.75, and you have 9
attending, then the cost is $88.9722.
Using setprecision(4) in the last cout statement can change
the final result to $88.97.
Operators
Operators
Operator Examples
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Auto increment and decrement
Target must be a variable (i.e., an l-value)
int i, j =10;
i = j++; /* i is 10, j is 11 */
i = ++j; /* i is 11, j is 11 */
i = j--; /* i is 10, j is 9 */
i = --j; /* i is 9, j is 9 */
i++, ++i, i--, and --i are legal (i.e., assignment is not required)
< May be embedded in expressions
< Often used in array indexes
Multiple assignment (i.e., the = operator returns a value)
< i = j = k = 0; /* equivalent to i = (j = (k = 0)) */
Operator Examples
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P?:
< a ? b : c; /* if a is true, then b, else c; a is usually
in parens */
< int max = (x > y) ? x : y;
Pop= (+=, -=, *=, /=, %=, ~=, <<=, >>=)
< variable op= expression; ø variable = variable
op expression;
< x += 10; ø x = x + 10;
< i -= 2; ø i = i - 2;
< a /= b; ø a = a / b;
< index %= size; ø index = index % size;
< mask <<= 2; ø mask = mask << 2;
Arithmetic Operators

Can be used for literal values and
variables (in order of precedence)
◦
◦
◦
◦
◦
◦
Parentheses( )
Multiplication *
Division /
Modulus%
Addition +
Subtraction –
Operators and Precedence

Which of the following is equivalent to mx + b ?
◦ (m * x) + b
◦ m * (x + b)

Operator precedence tells the order in which different operators in
an expression are evaluated.

Standard precedence order
◦ ( )
◦ * / %
◦ + -
Evaluated first, if nested then evaluate
the innermost first.
Evaluated second. If there are several,
then evaluate from left-to-right.
Evaluate third. If there are several,
then evaluate from left-to-right.
76
Relational Operators
Relational operators are used to compare two values to form a
condition.
Math
C++
Plain English
=
==
equals [example: if(a==b) ]
[ (a=b) means put the value of b into a ]
<

>


<
<=
>
>=
!=
less than
less than or equal to
greater than
greater than or equal to
not equal to
77
Operator Precedence
Which comes first?
Answer:
*
<
/
+
<=
==
%
>=
!=
>
=
78
Operator Precedence

If you were a computer, what would you
give as a result for:

y = 2 * 5 * 5 + 3 * 5 + 7;
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.
Programming Style (cont. )
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.
Example 0 – adding 2 numbers

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

Ali: Hey Mohamed, I just learned how to add two
numbers together.
Mohamed : Cool!
Ali : Give me the first number.
Mohamed : 2.
Ali : Ok, and give me the second number.
Mohamed : 5.
Ali : Ok, here's the answer: 2 + 5 = 7.
Mohamed : Wow! You are amazing!
after Mohamed says “2”, Ali has to keep this number in his mind.
after Mohamed says “5”, Ali also needs to keep this number in his mind.
First number:
2
Second number:
5
Sum:
7
The Corresponding C++ Program
#include <iostream>
using namespace std;
int main()
{
int first, second, sum;
cout << " Ali : Hey Mohamed, I just learned how to add”
<< “ two numbers together."<< endl;
cout << " Mohamed : Cool!" <<endl;
cout << " Ali : Give me the first number."<< endl;
cout << " Mohamed : ";
cin >> first;
cout << " Ali : Give me the second number."<< endl;
cout << " Mohamed : ";
cin >> second;
sum = first + second;
cout << " Ali : OK, here is the answer:";
cout << sum << endl;
cout << " Mohamed : Wow! You are amazing!" << endl;
return 0;
}
Write a program to convert a temperature in degrees
Fahrenheit to degrees Celsius.
Input(s)
fahrenheit
integer
Output(s)
celsius
double
OR
float
Additional Notes:
*Remark (General information about “float” and “double”):
• Both can be used for real numbers.
• The difference between double and float is their ranges.
• For memory efficiency, you should check their ranges and decide which one to
use for a variable.
Note that memory efficiency is not considered in our examples. Therefore,
double is used in general.
*Research Task:
Learn the ranges of float and double.
Relevant Formula
celsius=(5/9)*(fahrenheit – 32)
#include <iostream.h>
int main()
{
int fahrenheit;
double celsius;
cout<<"Please enter a temperature in degrees Fahrenheit :“;
cin>>fahrenheit ;
celsius= (5.0 / 9.0) * (fahrenheit - 32);
cout<<"The temperature in degrees Celsius is\n“<< celsius;
return 0;
}
Write a program that estimates the temperature in a
freezer (in Celsius) given the elapsed time (hours) since a
power failure. Assume this temperature (T) is given by
where t is the time since the power failure. Your
program should prompt the user to enter how long it
has been since the start of the power failure in whole
hours and minutes. Note that you will need to
convert the elapsed time into hours. For example, if
the user entered 2 30 (2 hours 30 minutes), you
would need to convert this to 2.5 hours.
Input(s)
hours
minutes
integer
integer
Output(s)
temperature
double
Relevant Formula
temperature=(4*time*time)/(time+2)-20
time=hours+minutes/60
#include <iostream.h>
int main()
{
int hours;
int minutes;
double time;
double temperature;
cout<<"Please enter the time : “;
cin>>hours>>minutes ;
time = hours + (double) minutes / 60;
temperature = ( 4 * time * time) / (time + 2) - 20;
cout<<"The temperature in freezer is \n“<< temperature;
return 0;
}
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
