lesson 2 - variables and data type

7/28/2019 Lesson 2 - Variables and Data Type

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What is a variable?

When a user enters a new value that would be involved in

the calculation, to manage that value, you can(temporarily) store it in the computer memory.

NAME

Data Type

Since the values entered in a reserved memory area changeregularly, they are called variables.

Creating a variable (Declaring a variable)

Type of the value (Data Type) Variable_Name;

Data


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Fundamental data typesWhen programming, we store the variables in our

computer's memory, but the computer has to knowwhat kind of data we want to store in them, since it isnot going to occupy the same amount of memory tostore a simple number than to store a single letter or alarge number, and they are not going to be interpretedthe same way.


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Name Description Size* Range*

charCharacter or smallinteger.

1bytesigned: -128 to 127unsigned: 0 to 255

short int(short)

Short Integer. 2bytes signed: -32768 to 32767unsigned: 0 to 65535

int Integer. 4bytes

signed: -2147483648 to2147483647unsigned: 0 to4294967295

long int(long)

Long integer. 4bytes

signed: -2147483648 to

2147483647unsigned: 0 to4294967295

boolBoolean value. It cantake one of two values:true or false.

1byte true or false

float Floating point number. 4bytes+/- 3.4e +/- 38 (~7digits)

doubleDouble precisionfloating point number.

8bytes+/- 1.7e +/- 308 (~15digits)

long doubleLong double precisionfloating point number.

8bytes+/- 1.7e +/- 308 (~15digits)

wchar_t Wide character. 2 or4 bytes 1 wide character


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Declaration of variables

In order to use a variable in C++, we must first declareit specifying which data type we want it to be. Thesyntax to declare a new variable is to write the specifierof the desired data type (like int, bool, f loat...)followed by a valid variable identifier. For example:

int a;float mynumber;


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Example 01// operating with variables#include

usingnamespace std;

int main (){// declaring variables:int a, b;int result;

unsignedshortint NumberOfSisters;signedint MyAccountBalance;short Year;}


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Scope of variables


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Initializing the variable When you have just declared a variable, it may not hold a

significant value.

To know the value it has, you should put an initial value into that

memory space. Putting an initial value is referred to as initializing the variable.

Initializing a created variable:

Type of the value(Data Type) Variable_Name;

Variable_Name = Value to be assign ;

type identifier (initial_value) ;


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Example 01// initialization of variables#include usingnamespace std;int main ()

{int a=5; // initial value = 5int b(2); // initial value = 2int c;c=4;

int result; // initial value undetermineda = a + 3;result = a - b;cout


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Introduction to strings

Variables that can store non-numerical values that arelonger than one single character are known as strings.


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// my first string

#include

#include

usingnamespace std;int main ()

{

string mystring = "This is a string";

cout


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// my first string#include

#include

usingnamespace std;

int main () {

string mystring;

mystring = "This is the initial string content";

cout


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Literals in C++ A literal is the source code representation of a fixed value literals are

represented directly in your code without requiring computation. A literal is any number, text or other information that directly

represents a value. Integer Literals

decimal formathexadecimal formatoctal format

The floating point Literals Character Literals Unicode escape sequence Boolean Literals


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Integer Literals 75 // decimal

0113 // octal

0x4b // hexadecimal 75 // int

75u // unsigned int

75l // long

75ul // unsigned long


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Floating Point Numbers 3.14159 // 3.14159

6.02e23 // 6.02 x 10^23

1.6e-19 // 1.6 x 10^-19 3.0 // 3.0

3.14159L // long double

6.02e23f// float


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Character and string literals

'z'

'p'

"Hello world" "How do you do?"


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Unicode escape sequence

\u0041' Capital letter A

'\u0030' Digit 0

'\u0022' Double quote "

'\u003b' Punctuation ;

'\u0020' Space

'\u0009' Horizontal Tab


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Boolean Literals

bool chosen = true;


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Defined constants (#define)

#define PI 3.14159

#define NEWLINE '\n'


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Example// defined constants: calculate circumference

#include usingnamespace std;#define PI 3.14159#define NEWLINE '\n'int main () {double r=5.0; // radius

double circle;circle = 2 * PI * r;cout


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Declared constants (const)

With the const prefix you can declare constants with aspecific type in the same way as you would do with avariable:

constint pathwidth = 100;

constchartabulator = '\t';

lesson 2 - variables and data type

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