meljun cortes c++_variables_keywords_data_types

8/10/2019 MELJUN CORTES C++_Variables_Keywords_Data_Types

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C++

Variables, Identifiers,

Keywords, Data Types

MELJUN CORTES MBA MPA BSCS


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MELJUN CORTES, MBA,MPA,BSCS

VARIABLES Is a location in the computers memory where

a value can be stored for use by a program. Is a symbol that represents a storage location

in the computers memory. A place to store a

piece of information. It must be declared with a name and a data

type before they can be used in a program.

Example:

integer1, sum, interger2, etc.


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NAMING CONVENTIONS

The names of variables in C++ are typically referred toas Identif iers. The following are rules for creating

identifiers. Names are made up of letters and digits.

The first character must be a letter or an underscore(_). However, an underscore is not recommended to

be used as the first character in a name since someof C++s internal identifiers begin with underscores.

C++ is case-sensitive, i.e., the lower-case letter a isnot the same as the uppercase letter A.

At least the first 31 characters of a name aresignificant.

There can be no spaces in identifiers. Ex. last_name

Keyword must NOT be used as identifiers because

they are part of C++ language.


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KEYWORDS These names are reserved and cannot be used for other

purposessuch as in naming user-defined variable names.The MS Visual C++ language has a total of 59 keywordsshown below.


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ESCAPE CODES

Are special characters that cannot be expressedotherwise in the source code of the program (all ofthem are preceded by an inverted slash (\))

\n newline \f page feed

\r carriage return \a alert (beep)

\t tabulation \ single quote ()

\v vertical tab \ double quote ()\b backspace \? question


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CONSTANTS

Constants are entities whose value does notchange.

A constant can either be numeric constant ora literal constant. In C/C++, a numeric

constant can be an integer or floating pointnumber, while a literal constant can be asingle character or a string, i.e. a constant

with more than one character. A singlecharacter is written such that it is enclosed ina pair of single quotes. A string is writtenenclosed in a pair of double quotes.



The Table 2.3 shows some examples of numeric and literalconstants. It is important to note that even if 'A' and "A"contains the same value, they are of different types. Theformer is a character while the latter is a string.



Basic Data Types in C++

A data type specifies the kind of valuescan be assumed by a variable of that type,the range of values that can be assumed

by a variable of that type, and the amountof memory (in bytes) needed by a variableto store a value of that type.

There are five basic data types in C++,namely: char, int, float, doubleand bool



charthe character data type. The chardata type is used to

represent/store/manipulate character datavalues. The range of values that can beassumed by a char value is from 0 to 255.

Example: a, B, c, name, Course, 7, *, $, etc.

intthe integer data type. The int data typeis used to represent/store/manipulate signedwhole numbers. The range of values that

can be assumed by an int value is from-2147483648 to 2147483647.

Example: 5, -10, 15, etc.



floatthe single precision floating point datatype. The float data type is used to store single

precision signed real numbers.Example: 6.20, 12.50, -21.489, 0.583, etc.

doublethe double precision floating point

data type. The double data type is used to storedouble precision signed real numbers.

Example: 5.10, 10.50, -15.356, 0.254, etc.

boolthe Boolean data type. The bool datatype is used to represent Boolean values trueorfalse.



The amount of memory spacerequired to store an int,a floatand doubleis platform-dependent (depends onthe machine and the software). For compilers such asthe Microsoft Visual C++ compiler, a charand boolrequires 1 byte of memory each, an in tand f loatrequires 4 bytes of memory each, while a doub lerequires 8 bytes of memory.

The sizeofis a keyword in C++. It is an operator that yields the size

in number of bytes of the specified data type.



Declaration of Variables

In order use a variable in C++, we must firstdeclare it specifying which of the data typeswe want it to be. The syntax to declare a

new variable is to write the data type specifierthat we want followed by a valid variableidentifier.



;

A semicolon signifies the end of a declaration. A missing

semicolon will cause the compiler to generate a syntaxerror. Variables should be named following the C++naming conventions. For example:

It is possible to declare several variables

of the same type on the same line. Insuch a case, a comma should be insertedbetween two variables. A missing commawill generate a syntax error. For example:charch1, ch2;

boolb1, b2;intx, y, z;

float degree_celsius,

degree_fahrenheit, degree_kelvin;

doublenumerator, denominator;

char ch;

boolb;inti;

floatf;

doubled;


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Additionally to this way of initializing variables

(known as c-like), C++ has added a new wayto initialize a variable: by enclosing the initialvalue between parenthesis ():

type ident i f ier(in it ial_value) ;For example:

int a (0);

Both ways are valid and equivalent in C++.


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Scope of Variables


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Scope of Variables

Global variablescan be referred toanywhere in the code, within any function,whenever it is after its declaration.

Local variablesis limited to the code levelin which they are declared. If they aredeclared at the beginning of a function (like inmain) their scope is the whole mainfunction.

In the example above, this means that ifanother function existed in addition to main(),the local variables declared in maincould notbe used in the other function and vice versa.


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In C++, the scope of a local variable is given

by the block in which it is declared (a block isa group of instructions grouped togetherwithin curly brackets {}signs). If it is declaredwithin a function it will be a variable with

function scope, if it is declared in a loop itsscope will be only the loop, etc...

In addition to localand globalscopes there

exists external scope, that causes a variableto be visible not only in the same source filebut in all other files that will be linked together


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Input / Output Functions

conso le

it is the basic interface of computers,normally it is the set composed of thekeyboard and the screen. The keyboard is

generally the standard inputdevice and thescreen the standard outputdevice.

In the iostreamC++ library, standard input

and outputoperations for a program aresupported by two data streams: cinfor inputand coutfor output.


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cout(the standard output stream )

it is normally directed to the screen.

it is used to output information to thescreen.

cin(the standard input stream)

it is normally assigned to the keyboard.

it is used to input information from thekeyboard.


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The cou tstreamis used in conjunction with theoverloaded operator


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The


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For examp le, these two sentences are very different:

cout


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cout


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Handling the standard input in C++ is done byapplying the overloaded operator of extract ion(>>) on the cinstream. This must be followedby the variable that will store the data that is

going to be read.For example:

int age;

cin >> age;

declares the variable age as an int and thenwaits for an input from cin (keyborad) in orderto store it in this integer variable.



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Always consider the typeof the variable thatare using as a container with cinextraction.If the variable is an integer then get an

integer, if variable is a character than get acharacter.



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MELJUN CORTES MBA MPA BSCS

meljun cortes c++_variables_keywords_data_types

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