3 Syntax Rules

8/22/2019 3 Syntax Rules

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Dr. Siti Barirah Ahmad Anas

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Room A.04.89

C++ Syntax Rules

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mailto:[email protected]



• C++ Program Structure – Keywords – Identifiers – Constant – ASCII Code – Character sets – Standard data types – Variable – Operators – Punctuators

• FormattedInput/Output

• Expression – Unary Expression

– Assignment Expression – Programming Examples

• Typedef and sizeofoperator

• Arithmetic conversion• Statement



• Technology Oriented • Business Driven • Sustainable Development • Environmental Friendly

• The rules of a programming language are called itssyntax

• Misusing the language is called a syntax error. Thecompiler will alert you to any syntax errors, all of whichmust be corrected

• If you speak the language perfectly, but your instructionsdon't generate the correct answer. This is called asemantic error

• Runtime error is when there occurs an expression which is

impossible to compute such as divide by 0 error




• A C++ program – Contains preprocessor directives that tells it how to

prepare program for compilation, e.g. #include

– Made of a global declaration sections with one or more functions

– Only one function should be named as main

– All functions are divided into 2 sections:• Definition section

– describe data to be used within the function – Local definition

• Statement section – Follows definition section – Contains set of instructions, called statement



Preprocessor directives

Global declarations

int main (void){

}

Local definitions

Statements

#include <iostream.h>

int a=1,b=2;

int main (void){

} // main

int c;

c=a+b;

return 0;

Example




• A C++ program is first constructed as a sequence of characterssuch as:

– uppercase letters => A to Z

– lowercase letters => a to z

– digits => 0 to 9

– special characters => + - * / = ( ) { } [ ]< > „ “ ! # % & _ | ^ ~ \ . , ; : ?

– white space character => blank, newline, tab

• These characters are collected by compiler into syntactic unitscalled tokens which are: keywords, identifiers, constant,operators and punctuators.




Keywords common to the C and C++ programming languages

auto break case char constcontinue default do double else

enum extern float for goto

if int long register return

short signed sizeof static struct

switch typedef union unsigned void

volatile whileC++-only keywords

and and_eq asm bitand bitor

bool catch class compl const_cast

delete dynamic_cast explicit export false

friend inline mutable namespace new

not not_eq operator or or_eq

private protected public reinterpret_cast static_cast

template this throw true try

typeid typename using virtual wchar_t

xor xor_eq




• Composed of a sequence of letters, digits andunderscore (_)

• The first character of identifier cannot be a digit• Case sensitive• Is a valid variable name

Valid Not validm not#meid 102_southidentifier2 -minus




• C++ manipulates various kinds of values.

• Basic types of constant consists of:

a) integer constant – integer valued number

• integer can be written in three different number system:

– decimal, octal or hexadecimal• range: -32768 to 32767

– decimal digits taken from set of 0 through 9eg: 0, 17, 9999

– octal digits taken from set of 0 through 7,however, first digit must be 0, eg: 0, 01, 0743,077777

– hexadecimalmust begin with 0x or 0Xfollowed by any combinations of digits 0through 9 and letters a through f (or A throughF ), eg: 0x, 0x1, 0x7FFF , 0xabcd




(b) floating point constant• base-10 number that contains either a decimal point or exponent (or

both)

• range: 3.4E-38 - 3.4E+38

• eg: 1.0, 3.1415, 0. , 1. , 2E-8, 1.6667E+8, 0.006e-3

(c) character constant• is a single character enclosed in single quotation marks• eg: „i‟, „z‟, „3‟, „?‟

• there are several character constant that expressed in terms of escapesequence eg: „\n‟, „\t‟, „\\‟, „\‟‟, „\”‟, „\‟




(d) string constant• a sequence of characters enclosed in double quotation marks• eg:

“abc”, “ ”, “Line 1\nLine 2\nLine 3”, “”

• string constants are stored by the compiler as arrays of characters

• 2 string constants separated only by white space are combined into onestring

• eg:

“abc” “def” = “abcdef”

(e) enumeration (enum)

• user defined constants

• eg:

enum day {sun, mon, tue, wed}




• Character from the character constantcomes from character set, supplied byhardware manufacturer

• ASCII – American Standard Code for Information

Interchange

– used by most computers

• EBCIDIC – Extended Binary Coded Decimal Interchange

Code

– used only by IBM Mainframes and their clones



Table 1:

ASCII Code




Written in C Name of character Integer value‘\a’ Alert 7

‘\\’ Backslash 92

‘\b’ Backspace 8

‘\r’ Carriage return 13

‘\”’ Double quote 34

‘\f’ Form feed 12

‘\t’ Horizontal tab 9

‘\n’ Newline 10

‘\0’ Null character 0

‘\’’ Single quote 39

‘\v’ Vertical tab 11




• Defines a set of values and a set of operationsthat can be applied on those values

• Standard/fundamental data types – char, int, double

• Derived types

– Pointer, enumerated type, union, array etc.




• What is… – Named memory locations – Have a type and size

• Declarations

– Used to name an object – E.g. char c;

• Definitions – Used to create an object

– E.g. char c = „a‟;

• Normally, declarations and definitions aredone at the same time



char code;

int i;

long national_debt;

float payRate;

double pi;

code

i

national_debt

payRate

pi

B

14

100000000000000

14.25

3.1415926536

Variable‟sIdentifier

Variable‟stype

Variable‟sIdentifier

program memory

Variables in Memory




• Initializer establishes the first value that thevariable will contain

• Example:int count = 0;

int count, sum = 0;

int count = 0, sum = 0;

int count = 0,

int sum = 0;

• When a variable is defined, it is not initialized,

the programmer must initialize the variable




• Arithmetic operators:

+ addition- subtraction* multiplication/ division% modulus

• Equality operators:

= = is equal!= not equal

• Relational operators:> greater than< less than

>= greater than or equal<= less than or equal

• punctuators: ( ) {} , ;

• parentheses immediately following main are not punctuator




• Operators have rules of precedence andassociativity that determine precisely howexpressions are evaluated.

• Precedence and associativity describe the order

in which each operator is evaluated by thecompiler.

• Precedence - -> determines the priority ofevaluation

• Associativity - -> determines the order in whichtwo or more operands with the same precedencewill be evaluated




• 1 + 2 * 3

» the value is 7

» * has higher precedence than +, causing themultiplication to be performed first, thenaddition.

• (1 + 2) * 3

» the value is 9» expressions inside parentheses are evaluated

first.

• 1 + 2 – 3 + 4 – 5

» The value is -1

» binary operators – and + have the sameprecedence, then use associativity rule “left toright”

• Refer table 2.

Table 2: Operator Precedence and Associativity



Table 2: Operator Precedence and Associativity

Operator Type Operator Execution Order

Primary Expression Operators () [] . -> expr ++ expr -- left-to-right

Unary Operators* & + - ! ~ ++expr --expr (typecast)

sizeof()right-to-left

Binary Operators

* / %

left-to-right

+ -

>> <<

< > <= >=

== !=

&

^

|

&&

||

Ternary Operator ?: right-to-left

Assignment Operators = += -= *= /= %= >>= <<= &= ̂ = != right-to-left

Comma , left-to-right




• Standard input file: keyboard• Standard output file: monitor

• Information from input and to output file will bebuffered in a storage area

Keyboard

Monitor

cin >>

cout <<

Memory

Buffer




• Purpose: display message on the monitor screen

• Syntax

cout >> “…” >> variable1 >>

• Examples

cout >> “Hello World!\n”

cout >> “The average value is” >> ave >> “\n”




• Output field can be set• Using #include <iomanip>

• Exampledouble x = 34.95;

cout << setw(8);

cout << setprecision(2);

cout << setprecision(2) << setw(8) << x;

• Output###34.95




• Purpose: read value from one/more variablesfrom the input

• Syntax

cin >> variable1 >> variable2 >> variable3

• Examples

cin >> first

cin >> first >> middle >> last

Khamis pagi 5 ogos? Saya OK no problem. Same venue UNITEN…? Time..?barirah




• Sequence of operands andoperators that reduces to a single

value e.g. 2 + 5• Expression type – primary, unary,

binary, etc.

• Precedence – determines the priority




• Primary expressions

– Identifier, constant and parentheticalexpression

– E.g. a, 7 and (2 + a - 3)

• Binary expressions

– Formed by operand-operator-operandcombination

– E.g. additive : a + 7 and multiplicative: 6/ 2




• Increment operator ++ and decrement operator --are unary operators with the same precedence asthe unary plus and minus, associate from right toleft.

• Occur in either prefix or postfix position, anddifferent effects may occur.

• ++i and i++ causes the stored value of i in memoryto be incremented by 1

• ++i increment i first then do expression (prefix)

• i++ do expression first then increment i (postfix)




• example:

int a, b, c = 0;

a=++c;

b=c++;

cout >> a >> b >> ++c;

note: ++ and -- cause the value of a variable in

memory to be changed




• Evaluates the operand on the right side of theoperator (=) and places the value in thevariable on the lefta = b + c;

• Assignment operators:= += -= /= %= >>= <<=

&= ?= |= – same precedence – right to left associativity

– changed value of variable – Left operand must be a single value




• Simple Assignment – As in algebraic expression

– E.g. a = 5, b = x + 1, i = i + 1

• Compound assignment – Shorthand notation for a simple expression

– E.g. x *= y equals to x = x * y

• Example – x *= y + 3 evaluated as x = x * (y + 3)




• E.g.1

int a, b = 2, c = 3;

a = b + c;

• E.g. 2a=b=c=0; equivalent to a=(b=(c=0));

k += 2; k=k+2;

j *= k + 3; j=j * (k+3);




int a=3, b=4, c=5, x, y;

x = a * 4 + b / 2 - c * b;

y = --a * (3 + b) / 2 - c++ * b;

What is the new value of each variableafter executing the above expressions?




• allows programmer to associate a type withan identifier

• eg: typedef char uppercase;

typedef int inches;

uppercase u;

inches length, width;

• uses:

– have type names that reflect the intended use

t y p e d e f




s i z e

o f

• a unary operator to find the number of bytes needed to store an objectin memory.

• sizeof (object)• note: object can be a type,

expression, an array or structure type

• eg: sizeof (char) = 1




• Used for mixed type expression – E.g. int + float

• 2 conversion types – Implicit type conversion

• Type is automatically converted by C++program

• Based on the promotion hierarchy

– Explicit type conversion

• Uses cast expression operator e.g. (int) a

• Type is converted by the programmer



char

short

int

Unsigned int

Long int

Unsigned long int

float

double

Long double

The Promotion Hierarchy




• A.k.a. casting

• Example

– (float) a – (float) (x + y)

– (float) (a / 10)

– (float) a / 10




• Causes an action to be performed inC++ program

• 6 types altogether but concentrate

on the first two: – Expression statement

• Expression ended with semicolon

– Compound statement• Unit of code between the opening and

closing braces




• Statements and defined constant – Common error:

#define PI 3.142;

...

area = PI*r*r;

– Actual evaluation is

area = 3.142;*r*r;

3 Syntax Rules

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