1. សាកលវិទ្យាល័យជាតិគ្រប់គ្រង National University of Management
Variable and data type
Lectured by : SRENG VICHET
Tel :
Prepared by : CHEA VICHET
EAV DARAPISAL
CHONG KIMKEANG
SRENG VICHET
ចំនាយពេល ៣ម៉ោង

2. National University of Management
Objectives
Identifier
Variable and data type
Declared Variable
initialization Variable
Scope of Variable
Introduction to string
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Objective (con’t)
string concatenate
Constant variable
Literal variable
Symbolic Constant
typedef
Enumerated Constants
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4. National University of Management
Let’s think!
If I want you remember number 5 then number 2 more, so your brain remember number 5 and number 2.
Now I suggest you to add 1 in the first number. You ready answer 6(5+1), then take number one minus number two. The result is 6 -2 =4.
first_num = 5;
second_num = 2;
first_num+=1;
int result = first_num –second_num;
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Identifier
Name of variable or function
Must begin with letter.
No space.
Must not be matched any keywords.
first_number = 5; // valid
Second number = 2 // invalid identifer
Case sensitive
Result = 7;
result = 7;
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Variable & Data Type
Variable:
Identifier that is used to store any different data type.
mySkill =“information technology”;
myAge = 28;
myHeight =1.70;
Data Type
It is the type of data that variable will be stored:
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Fundamental Data Type
Character variables hold a single byte representing 1 of the 256 characters and symbols in the standard ASCII character set.
for (int i=1; i<128; i++) {
cout << char(i)<<endl; }
cout << "The size Max of short int is :"<<SHRT_MAX<<endl;
cout << "The size Min of short int is :"<<SHRT_MIN<<endl;
cout << "The size Max of int is :"<<INT_MAX<<endl;
cout << "The size Min of int is :"<<INT_MIN<<endl;
cout << "The size Max of long int is :"<<LONG_MAX<<endl;
cout << "The size Min of long int is :"<<LONG_MIN<<endl;
cout << "The size Max of Float is :"<<FLT_MAX<<endl;
cout << "The size Min of Float is :"<<FLT_MIN<<endl;
cout << "The size Max of Double is :"<<DBL_MAX<<endl;
cout << "The size Min of Double is :"<<DBL_MIN<<endl;
cout << "The size Max of Long Double is :"<<LDBL_MAX<<endl;
cout << "The size Min of Long Double is :"<<LDBL_MIN<<endl;
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Declared Variable
Syntax: <data type> <identifier>;
int numberOfEmployee;
float salary;
char letter;
string name;
Multiple variable with the same type:
int a,b,c;
float salary, income;
ASCII =255
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9. Initialization of variable
When declaring a regular variables, its value is by default undermined. In order to initialize the variable, we have two ways to to do this in C++:
Syntax:
type identifier = initial_value; //c-like
int a = 0;
type identifier(initial_value); // constructor initialization
int b(0);
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10. National University of Management
singed and unsigned
char, short, long and int can be signed and unsigned too.
singed : your variables are stored the positive(+) and negative(-) values;
unsigned : your variable are stored the positive(+) and value of 0;
unsigned short int myNumberOfSisiters;
signed int myAccountBalance;
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Example
#include <iostream> int main() { unsigned short ageP=30; int ageN=-30; std::cout << ageP<<std::endl; std::cout << ageN<<std::endl; std::cin.get(); return 0; }
unsigned short age =-10; // logical error
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12. National University of Management
Scope of Variable
local variable may be accessed within the block of code in which a variable may be accessed. It can be used in function or a block of code({}).
global variable may be accessed within every scope of the program. It can be used everywhere even though in function.
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13. National University of Management
#include <iostream>
using namespace std;
int a; // global variable
int b; // global variable
int main () {
int result; // local variable
a = 5; // you use
b = 2; // global
result = a + b ; // variable here
cout << "a + b = " ;
cout << result ;
cin.get();
return 0; }
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14. National University of Management
#include <iostream>
using namespace std;
int a, b; //global variable
int main() {
a = 5;
b = 10;
cout << "a = " << a << endl;
cout << "b = " << b << endl;
int a, b; //local variable to its block
a = 2;
b = 3; }
cin.get();
return 0;
a = 5
b = 10
a = 2
b = 3
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15. Introduction to string
Variables that can store non-numberical values that are longer than one single character are known as string.
In order to used string type we need to include a additional header file in our source code: <string>.
#include <string>
…..
string num=“National University of Management”;
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#include <iostream> #include <string> using namespace std;   int main () { string mystring = “This is a string.” cout << mystring << endl; string yourstring(“This is another string.”); cout << yourstring ; return 0; }
This is a string.
This is another string.
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17. National University of Management
string concatenate
string firstName = "Sabay"; string middleName = "Sok"; string lastName = "Sen"; string fullName = lastName + " "+ middleName + " "+ firstName; cout << fullName; cout << endl;
Concatenate : ការតភ្ជាប់អក្សរ a series of events, ideas or things that are not connected
ចប់
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Constant Variable
A constant, like a variable, is a memory location where a value can be stored. Unlike variables, constants never change in value(read-only).
C++ has two type of constants:
Literal constants.
Symbolic constants.
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19. National University of Management
Literal Constant
Is a value typed directly into your program wherever it is needed.
Integer
75 // int
75u // unsigned int
75l // long
75ul // unsigned long
Literal Constant ជាតួអក្សរ លេខ ឬព្យញ្ជនៈ ដែលមានតំលៃ និងប្រភេទរបស់ ខ្លួនវាជាក់លាក់
long width = 5;
This statement assigns the integer variable width the value 5. The 5 in the statement
is a literal constant. You can’t assign a value to 5, and its value can’t be changed.
The values true and false, which are stored in bool variables, also are literal constants.
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20. Literal Constant (con’t)
Floating Point //
6.02e23 // 6.02 x 1023
L // long double
6.02e23f // float
Character and String
'z' // 'z' character
“Hello World” // “Hello World” String
Boolean
Boolean has only two value : true (1) និង false (0)
for (int i=1; i<128; i++) {
cout << char(i)<<endl; }
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Symbolic Constant
Is a constant represented by a name, just like a variable. The const keyword precedes the type, name, and initialization.
const int bouns = 300;
const float pi = ;
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22. typedef (synonym of type definition)
typedef int integer; //integer is synonym int
typedef double salary; //salary is synonym double
typedef salary mysalary; //incorrect
Why we used typedef:
In order to hide data type.
Easy to know, understand and use data type.
typedef int integer;
typedef double salary;
integer myAge=13;
salary mySalary=120;
cout << "Your age is :"<<myAge<<endl;
cout << "Your salary is :"<<mySalary<<endl;
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23. National University of Management
Enumerated Constants
It create a set of constants with a single statement. They are defined with the keyword enum followed by a series of comma-separated names surrounded by braces:
enum COLOR {RED, BLUE,GREEN,};
The values of enumerated constants begin with 0 for the first in the set and count upwards by 1.
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24. National University of Management
Example
int Mon=1;
int Tue=2;
int Wed=3;
int Thu=4;
int Fri=5;
int Sat=6;
int Sun=7;
enum DAYOFWEEK {
Mon=1,
Tue,
Wed,
Thu,
Fri,
Sat,
Sun, };
DAYOFWEEK dayOfWeek= Sun;
cout << dayOfWeek; //7
enum DAYOFWEEK {
monday=1,
tuesday,
wenesday,
thursday,
friday,
saturday,
sunday };
DAYOFWEEK today=sunday;
cout << "Today is :"<<today<<endl;//7
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25. National University of Management
Quiz
Please list all data types that you know, at least 5 data types.
What is distinguish between singed and unsigned?
What is the difference between an integer variable and a floating variable.
Which of the following variable names good, bad, invalid?
Age
!Ex
R98
_Invalid
----- Meeting Notes (9/27/12 09:46) ----- 13
ch02 data type
scope variable 17
using variable
constant variable 27
ch03 operator
arithmetic operator
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26. National University of Management
Thank You!
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