Lecture02(1)

OBJECTIVES
In this lecture you will learn:
To write simple computer programs in C++.
To write simple input and output statements.
To use fundamental types.
Basic computer memory concepts.

Introduction
C++ Programming
Facilitates disciplined approach to computer program design
Programs process information and display results
Examples Demonstrate
How to display messages
How to obtain information from the user

First Program in C++: Printing a Line of Text
Simple Program
Prints a line of text
Illustrates several important features of C++

Outline
fig02_01.cpp
(1 of 1)
fig02_01.cpp
output (1 of 1)

Good Programming Practice
Every program should begin with a comment that describes the purpose of the program, author, date and time.

Common Programming Error
Forgetting to include the
header file in a program that inputs data from the key­board or outputs data to the screen causes the compiler to issue an error message, because the compiler cannot recognize references to the stream components (e.g. cout).

Common Programming Error
Syntax errors are also called compiler errors, compile-time errors or compilation errors, because the compiler detects them during the compilation phase. You will be unable to execute your program until you correct all the syntax errors in it. As you will see, some compilation errors are not syntax errors.

Tokens: The smallest individual units of a program are called tokens.
Constants
Variables
Keywords
Data Types
A C++ program is written using these tokens, white spaces , and the syntax of the language.

Constants , Identifiers and Keywords
The alphabets , numbers and special symbols when properly combined form constants , identifiers and keywords.
Constant: a constant is a quantity that does not change. This can be stored at a location in memory of computer.
Variable(identifiers) : is considered as a name given to the location in memory where this constant is stored. Naturally the contents of the variable can change. There are fundamental requirement of any language. Each language has its own rules for naming these identifiers.

Following are the rules for naming identifiers:
Only alphabetic characters digits and underscores are permitted.
The name cannot start with a digit.
Uppercase and Lowercase letters are distinct
A declared keyword cannot be used as a variable name.
For Example:
3X + Y = 20

Keywords
Keywords implement specific C++ language features.
They are explicitly reserved identifiers and cannot be
used as names for the program variables or other
user defined program elements.

Data Type
Data Type : type of data to be stored in a variable
Primitive data type (built-in data type): provided as an integral part of the language
Integer type
Real type
int val;

Primitive Data Type
Primitive Type
I
N
T
E
G
E
R
R
E
A
L
or more
big
or more

Primitive Data Type
Why do we need to define the type of data?
Efficient use of memory space
Data loss can happen when store big data into small memory space

Primitive Data Type
sizeof operator
Return memory size of operand in byte
Need () when the operand is data type
Otherwise () is optional
#include
using namespace std;
int main(void)
{
int val=10;
cout << sizeof val << endl;// print memory size
cout << sizeof(int) << endl;// print int data type
return 0;
}

Primitive Data Type
Criteria of selection of data type
Real type data
Accuracy
‘double’ is common

Primitive Data Type
Example
#include
#include
using namespace std;
int main(void)
{
double radius;
double area;
cout << "Input radius of circle" << endl;
cin >> radius;
area = radius * radius * 3.1415;
cout << area;
return 0;
}

Primitive Data Type
unsigned: the range of data is changed
Positive integer only
Can not be used in real data type

Primitive Data Type
How to express letter (including characters, notations, …) inside computer?
ASCII (American Standard Code for Information Interchange) code was born for expressing letters.
Defined by ANSI (American National Standard Institute)
The standard of letter expression by computer
Ex) letter ‘A’ ? 65, letter ‘B’ ? 66

Primitive Data Type
Range of ASCII code
0 ~ 127, ? possible using ‘char’ type
Declare ‘char’
Expression of letters
‘’ (quotation mark)

Primitive Data Type
Example
#include
using namespace std;
int main(void)
{
char ch1='A';
char ch2=65;
cout << ch1 <
cout << (int)ch1 << endl << (int)ch2 <
return 0;
}

Primitive Data Type
ASCII code

Symbolic Constant
Make ‘variable’ to ‘constant’
#include
using namespace std;
int main(void)
{
const int MAX = 100;
const double PI = 3.1415;
return 0;
}

Another C++ Program: Adding Integers
Variables
Location in memory where value can be stored
Common data types (fundamental, primitive or built-in)
int – integer numbers
char – characters
double – floating point numbers
Declare variables with name and data type before use
int integer1;
int integer2;
int sum;

Another C++ Program: Adding Integers (Cont.)
Variables (Cont.)
Can declare several variables of same type in one declaration
Comma-separated list
int integer1, integer2, sum;
Variable names
Valid identifier
Series of characters (letters, digits, underscores)
Cannot begin with digit
Case sensitive (upper and lower case letter)
Keywords

Outline
fig02_05.cpp
(1 of 1)
fig02_05.cpp output (1 of 1)
Declare integer variables
Use stream extraction operator with standard input stream to obtain user input
Stream manipulator std::endl outputs a newline, then “flushes output buffer”
Concatenating, chaining or cascading stream insertion operations

Good Programming Practice
Place a space after each comma (,) to make programs more readable.

Good Programming Practice
Some programmers prefer to declare each variable on a separate line. This format allows for easy insertion of a descriptive comment next to each declaration.

Portability Tip
C++ allows identifiers of any length, but your C++ implementation may impose some restrictions on the length of identifiers. Use identifiers of 31 characters or fewer to ensure portability.

Good Programming Practice
Choosing meaningful identifiers helps make a program self-documenting—a person can understand the program simply by reading it rather than having to refer to manuals or comments.

Good Programming Practice
Always place a blank line between a declaration and adjacent executable statements. This makes the declarations stand out in the program and contributes to program clarity.

Another C++ Program: Adding Integers (Cont.)
Input stream object
std::cin from
Usually connected to keyboard
Stream extraction operator >>
Waits for user to input value, press Enter (Return) key
Stores value in variable to right of operator
Converts value to variable data type
Example
std::cin >> number1;
Reads an integer typed at the keyboard
Stores the integer in variable number1

Another C++ Program: Adding Integers (Cont.)
Assignment operator =
Assigns value on left to variable on right
Binary operator (two operands)
Example:
sum = variable1 + variable2;
Add the values of variable1 and variable2
Store result in sum
Stream manipulator std::endl
Outputs a newline
Flushes the output buffer

Another C++ Program: Adding Integers (Cont.)
Concatenating stream insertion operations
Use multiple stream insertion operators in a single statement
Stream insertion operation knows how to output each type of data
Also called chaining or cascading
Example
std::cout << "Sum is " << number1 + number2 << std::endl;
Outputs "Sum is “
Then, outputs sum of number1 and number2
Then, outputs newline and flushes output buffer

Memory Concept
Variable names
Correspond to actual locations in computer's memory
Every variable has name, type, size and value
When new value placed into variable, overwrites old value
Writing to memory is destructive
Reading variables from memory nondestructive
Example
sum = number1 + number2;
Value of sum is overwritten
Values of number1 and number2 remain intact

Fig. 2.6 | Memory location showing the name and value of variable number1.

Fig. 2.7 | Memory locations after storing values for number1 and number2.

Fig. 2.8 | Memory locations after calculating and storing the sum of number1 and number2.

Arithmetic
Arithmetic operators
*
Multiplication
/
Division
Integer division truncates remainder
7 / 5 evaluates to 1
%
Modulus operator returns remainder
7 % 5 evaluates to 2

Common Programming Error
Attempting to use the modulus operator (%) with non integer operands is a compilation error.

Arithmetic (Cont.)
Straight-line form
Required for arithmetic expressions in C++
All constants, variables and operators appear in a straight line
Grouping subexpressions
Parentheses are used in C++ expressions to group subexpressions
Same manner as in algebraic expressions
Example
a * ( b + c )
Multiple a times the quantity b + c

Fig. 2.9 | Arithmetic operators.

2.6 Arithmetic (Cont.)
Rules of operator precedence
Operators in parentheses evaluated first
Nested/embedded parentheses
Operators in innermost pair first
Multiplication, division, modulus applied next
Operators applied from left to right
Addition, subtraction applied last
Operators applied from left to right

Common Programming Error 2.4
Some programming languages use operators ** or ^ to represent exponentiation. C++ does not support these exponentiation operators; using them for exponentiation results in errors.
Use pow(A, B) = A^B function in C++

Fig. 2.11 | Order in which a second-degree polynomial is evaluated.

Decision Making: Equality and Relational Operators
Condition
Expression can be either true or false
Can be formed using equality or relational operators
if statement
If condition is true, body of the if statement executes
If condition is false, body of the if statement does not execute

Fig. 2.12 | Equality and relational operators.

Common Programming Error 2.5
A syntax error will occur if any of the operators ==, !=, >= and <= appears with spaces between its pair of symbols.

Common Programming Error
Reversing the order of the pair of symbols in any of the operators !=, >= and <= (by writing them as =!, => and =<, respectively) is normally a syntax error. In some cases, writing != as =! will not be a syntax error, but almost certainly will be a logic error that has an effect at execution time. (cont…)

Outline
fig02_13.cpp
(1 of 2)
using declarations eliminate need for std:: prefix
Can write cout and cin without std:: prefix
Declare variables
if statement compares values of number1 and number2 to test for equality
If condition is true (i.e., values are equal), execute this statement
if statement compares values of number1 and number2 to test for inequality
If condition is true (i.e., values are not equal), execute this statement
Compares two numbers using relational operator < and >

Outline
fig02_13.cpp
(2 of 2)
fig02_13.cpp output (1 of 3)
(2 of 3)
(3 of 3)