Welcome to CPSC 206

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Structured Programming in CStructured Programming in C

Welcome to CPSC 206Welcome to CPSC 206

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Lecture Information

http://people.cs.tamu.edu/ychen/Teaching/CPSC206

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Lecture Topics:

0. Introduction to Computer Science1. Overview of C Ch 1, 2

2. Flow of control and functions Ch 3, 43. Character processing & fundamental data types Ch 5, 64. File I/O Ch 135. Pointers, Arrays, and Strings Ch 8, 9, 106. Structures, and linked lists Ch 12

Features of C:Features of C:

7. Enumeration type and storage classes Ch 7, 88. Recursion Ch 11

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Review of Class on Sept. 14, Tuesday

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An Overview of C— Chapter 1

A brief history of C Features of C Get Ready to Program A First Program The Basics of C Programming

Variables, Expressions, and AssignmentsInitialization Preprocessing directives: #define and #include Print and Read formatted data: printf() and scanf() The while statement

Problem Solving: Computing Sums Style, Programming Errors and System Considerations.

A Depth Program: Algorithm and codeDissection of the depth program

Declarationmain Functionprintf function

Basics of C ProgrammingGeneral form of a program

DeclarationVariableExpressionData Type and Operation

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The general form of a programThe general form of a programpreprocessing directivesint main (){

declarations statements

}

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DeclarationsDeclarationsPurpose: Tell the compiler what kind of data can be stored in each of the variables.

The compiler can set aside the appropriate amount of memory to hold the data.

Format:Data_Type Variable1, Variable2;

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VariablesVariablesA variable name can be a sequence of letters, digits, and underscores.A variable name may not begin with a digit.Certain keywords, also called reserved words, cannot be used as names of variables.

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ExpressionsExpressionsHow to use expressions?

on the right side of assignmentArguments to functions

How to construct an expression?ConstantsThe name of a variableMeaningful combinations of operators with variables and constants

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Integer:Integer:Division a/b: an integer expression divided by another integer expression yields an integer value.

Any fractional part is discarded.Modulus a%b: the remainder after a is divided by b.If a or b is negative, the results of division and modulus are system-dependentIn a/b and a%b, the value of b cannot be zero.

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Character:Character:Constants are written within single quotesExample:

‘A’ ‘1’

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Floating types:Floating types:float: an F suffix

1.22Fdouble: unsuffixed floating constant

1.22long double: an L suffix

1.22L

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An Overview of C— Outline


Variables, Expressions, and Assignments Initialization Preprocessing directives: #define and #include Print and Read formatted data: printf() and scanf() The while statement


InitializationInitializationA variable can be initialized when it is declared.Constants or constant expressions can be used to initialize a variable.Declared variables can be used to initialize a variable.

a variable cannot be used before it has been declared.

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Preprocessing directives:Preprocessing directives:

#include “filename”The preprocessor replaces the line with a copy of the named file.

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An Overview of C— Outline A brief history of C Features of C Get Ready to Program A First Program The Basics of C Programming



Preprocessing directives:Preprocessing directives:

#define A BIt affects only those lines in the file that come after it.All occurrences (after this line) of the identifier A, except in quoted string, will be changed to B.

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Print and Read formatted dataPrint and Read formatted data

Arguments: control_string and other_arguments

control_string contains formats, called conversion specifications, which are matched with other arguments.

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How to specify format using conversion specification?

%field_widthconversion_character%field_width.precisionconversion_characterconversion_character: how the data is

printed?o c: as a charactero d: as a decimal integero f: as a floating-point number

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Example: scanf(“%d”, &x); &: address operator%d — how to interprete the input stream

the input characters typed at the keyboard is interpreted as a decimal integer

&x — where to store the valuethe value of the decimal integer is stored at the address of x.

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The while statementThe while statementwhile (expression)

statementstatement is executed as long as the value of expression is true

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Review of Class on Sept. 14, Tuesday

End

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Chapter 2:

Lexical Elements, Operators, and the C System

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Introduction

C is a language.

Lexical Elements, Operators, and the C SystemLexical Elements, Operators, and the C System

C has an alphabet

C has rules for putting together words and punctuation to make legal programs.

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Introduction

C is a language. C has an alphabet

Lowercase letters: a b c …… zUppercase letters: A B C …… ZDigits: 0 1 2 3 4 5 6 7 8 9 Other characters:

o + - * / = ( ) { } [ ] < > ‘ “ ! @ # $ % & _ | ^ ~ \ . , ; : ?

White space characters: o blank, newline, tab, etc.


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Introduction

C is a language. C has rules for putting together words and

punctuation to make legal programs. These rules are called syntax


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Introduction

C is a language Alphabet syntax

What is C program?A C program is a sequence of characters


How a computer understands this sequence of characters?

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Introduction

Compiler

C code Preprocessor

object code

errors

Loader

Machine code


How does a compiler know whether a C program is correct or not?

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Introduction

How to check a C program is correct? Compiler

The program that checks the legality of a program.

How compiler checks the legality of a program?The characters are collected by the

compiler into syntactic units called tokensThe compiler checks whether the tokens

can be formed into legal strings according to the syntax of C language.


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Introduction

In C language, there are six kinds of tokens:

Keywords Identifiers Constants String constants Operators Punctuators


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Outline

An Example — Characters and Lexical ElementsLexical Elements

Comments Keywords Identifiers Constants String Constants Operators and Punctuators

An Example: Computing Powers of 2The C System


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An Example — Characters and Lexical Elements

/* Read in two scores and print their sum. */

#include <stdio.h>

int main(void){ int score_1, score_2, sum;

printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0;}

sum.cComment: be replaced with a single blank


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#include <stdio.h>



sum.c

File stdio.h is included


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sum.c

A Copy of stdio.h

Keyword: int void

Identifier: mainscore_1score_2sum

Operator: Parentheses ( )

Punctuators: ; ,{


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An Example — Character and Lexical Elements

How the compiler distinguishs tokens? white space

For example: int score_1s



What if we write as follows?intscore_1, score_2, sum;

The compiler considers intscore_1 as a single token.

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/* Read in two scores and print their sum. */

#include <stdio.h>

int main(void){ intscore_1, score_2, sum;


sum1.c


% gcc sum1.csum1.c: In function `main':sum1.c:8: error: `intscore_1' undeclared (first use in this function)sum1.c:8: error: (Each undeclared identifier is reported only oncesum1.c:8: error: for each function it appears in.)sum1.c:8: error: `score_2' undeclared (first use in this function)sum1.c:8: error: `sum' undeclared (first use in this function)sum1.c:11: error: `score_1' undeclared (first use in this function)

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sum.c

A Copy of stdio.h

Identifier: printfscanf

Operator: ( )&

Punctuators: ,;

String ConstantA series of characters enclosed in “ ”


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sum.c

A Copy of stdio.h

Identifier: sumscore_1score_2

Operator: + =

Punctuators: ;

Constant0


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An Example — Characters and lexical Elements

Summary Tokens:

Keyword: int voidIdentifier: printf scanf sumOperator: ( ) &Punctuators: ;}Constant: 0String Constant: “Input two scores as

integers: “ Separate two tokens: white space


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Outline





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Comments

What is comment? Arbitrary strings of symbols placed between

the delimiters /* and */. Single line comment: // text

How compiler processes comments? The compiler changes each comment into a

single blank character.Why comment?

Comments are used by the programmer as a documentation aid.

Lexical Elements, Operators, and the C SystemLexical Elements, Operators, and the C SystemLexical Lexical ElementsElements

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Comments

Rule1: Where can we place comments? Anywhere?

NoCompiler replaces each comment by a

single blank character o Comments can be placed wherever a single

blank character can appear. Example

x = 10+/* add the numbers */5;

x = 10+ 5;


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Comments


#include <stdio.h>

int main(void){ int/* a comment*/x;

x=10+5; printf("x=%d\n",x);

return 0;}

comment.c

int x;

% gcc comment.c% a.outx=15

Lexical Lexical ElementsElements

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Comments

Question: Can a comment appear in the middle of a keyword or identifier? Compiler will insert a single blank

character into a keyword or identifier Since a blank is used to separate two

tokens, the keyword or identifier will be considered as two tokens.

No


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Comments


#include <stdio.h>

int main(void){ int x, x/* a comment */y; return 0;}

comment1.c

% gcc comment1.ccomment1.c: In function `main':comment1.c:6: error: redeclaration of `x'comment1.c:6: error: `x' previously declared herecomment1.c:6: error: parse error before "y"

int x, x y;


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Comments

Rule2: nested comments Multi-Line comments may not be nested.

Example:/* outer comment /* inner comment */ */

A single-line (//) comment can be nested within a multi-line comment.Example:

/* a //test of nested comments. */


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CommentsAn understanding of Rule2:Usually when a compiler encounters a pair /*,

it considers text between this /* and the first occurrence of */ after this /* as a comment;

this comment is replaced by a blank character.


/* outer comment /* inner comment */ */

/* a //test of nested comments */


*/

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Comments


#include <stdio.h>

int main(void){ int x=1; /* This is a comment /* */ return x;}

comment3.c#include <stdio.h>

int main(void){ int x; /* //*/ return 0;}

comment2.c


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Comment

Summary What is comment?

Arbitrary strings of symbols placed between the delimiters /* and */.

Single line comment: // text The compiler changes each comment into a

single black character. Rules:

Multi-line comments cannot be placed in the middle of a keyword or identifier.

Multi-line comments may not be nested.


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Outline





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Keywords

What is Keywords? Keywords are explicitly reserved words that

have a strict meaning as individual tokens in C.

Examples of Keywords Data Type: int, char, long, short

Compared to other major languages, C has only a small number of keywords.

C is small


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Keywords

Rules: Keywords cannot be redefined or used in

other contexts. Example:

keywords cannot be used as variable names.


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Outline





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Identifiers

What is identifier? The names of variables, functions, labels

and other user-defined items are called identifier.

Examplesint main(void)int score_1, score_2, sum;


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Identifiers

Special identifier Keywords can be thought of as identifiers

that are reserved to have special meaning in the C language.

The names of functions in standard library would not be redefined.

The identifier main is special — C programs always begin execution at the function called main.


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Identifiers

Rules:1. An identifier is a token that is composed of

a sequence of letters, digits, and underscore _ .

2. A letter or underscore must be the first character of an identifier. Valid identifier: a, b, c Invalid identifier: a_...b, 1a


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Identifiers

Rules (contd.):3. Case-sensitive

Identifiers C and c are different4. Would not be defined as a keyword. It is not recommended to define a variable

name as the name of a function in the standard library and the identifier main. Example: define a variable name as

printf;5. Identifiers should be chosen to reflect their

use in the program.


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Identifiers

Examples of invalide identifiers: Rule1:

o int a_...b; Rule2:

o int 1a; Rule3:

o int c;o C =0;

Rule4: o int char;o int printf;


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Identifiers


#include <stdio.h>int main(void){ int a_...b; int 1a; int c; int char; int printf; C=0; printf("A test of identifiers\n"); return 0;}

identifier.c

% gcc identifier.cidentifier.c: In function `main':identifier.c:4: error: syntax error before '...' tokenidentifier.c:5:13: invalid suffix "a" on integer constantidentifier.c:7: warning: useless keyword or type name in empty declarationidentifier.c:7: warning: empty declarationidentifier.c:9: error: `C' undeclared (first use in this function)identifier.c:9: error: (Each undeclared identifier is reported only onceidentifier.c:9: error: for each function it appears in.)identifier.c:10: error: called object is not a function


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Identifiers

Summary What is identifier?

The names of variables, functions, labels and other user-defined items are called identifier.

Special identifier Keywords, names of functions in C library,

main Rules:

1. composed of letters, digits, and underscore _ .2. The first character must be a letter or

underscore.3. case-sensitive4. would not be defined as the special identifiers.


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Outline





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Constants

What is a constant? Constants refer to fixed values that the

program may not alter. Examples:

Integer constants: 0, 17 Floating constants: float, double, long double

1.0, 3.14 Character constants: (enclosed between single

quotes)‘a’, ‘A’‘\n’ : newline



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Constants

Integer constants Decimal integer Octal integer Hexadecimal integer



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Constants

Octal Integer: What is the decimal value of an octal integer?

An octal integer a= ik-1 ik-2 …..i0o The decimal value is

ik-1* 8k-1 + ik-2 * 8k-2 + …..+ i0 * 80

Example:o The decimal value of an octal integer

a = i3i2i1i0=7121 is 7 * 83 + 1 * 82 + 2* 81 + 1 * 80 =3665



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Constants

Hexadecimal Integer: What is the decimal value of a hexadecimal

integer? A hexadecimal integer a= ik-1 ik-2 …..i0

o The decimal value is ik-1* 16k-1 + ik-2 * 16k-2 + …..+ i0 * 160

Example:o The decimal value of a hexadecimal integer

a = i3i2i1i0=7121 is 7 * 163 + 1 * 162 + 2* 161 + 1 * 160 =28961



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Constants

Representation of Integer constants Decimal integer: 17 Octal integer:017 Hexadecimal integer: 0x17



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Constants

Integer constants

#include <stdio.h>int main(void){ printf("17=%d 017=%d 0x17=%d\n", 17, 017, 0x17); return 0;}

constant.c

% gcc constant.c% a.out17=17 017=15 0x17=23



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Constants

An integer may be too large to be stored in a machine word. 123456798900 may be too large

The maximum integer is defined in head file <limits.h> INT_MAX



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Constants#include <limits.h>#include <stdio.h>int main(void){ printf("123456789000=%d\n", 12345678900); printf("The maximum integer is %d \n", INT_MAX); return 0;} % gcc constant1.c

constant1.c: In function `main':constant1.c:5: warning: integer constant is too large for "long" type% a.out123456789000=2The maximum integer is 2147483647

constant1.c



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Constants

Summary Integer constants: 0, 17

Decimal integer: 17Octal integer: 017Hexadecimal integer: 0x17An integer may be too large to be stored

in a machine word. Floating constants: 1.0, 3.14 Character constants: (enclosed between single

quotes)



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Outline





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String Constants

What is string constant? A sequence of characters enclosed in a pair

of double quote marks.

Example: “a string of text” “” // the null string “ ” // a string of a blank character



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String Constants

String constants are stored by the compiler as arrays of characters, ended by the null character ‘\0’. “Hello” | H | e | l | l | o | \0 |

String constants are differently form character constants. “a” ≠‘a’



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String Constants

#include <stdio.h>int main(void){ char c; c = "a string"; return 0;}

% gcc string_char.cstring_char.c: In function `main':string_char.c:5: warning: assignment makes integer from pointer without a cast



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String Constants

Special characters in string constants Double quote “

\”Example: “a string with double quotes \””

Backslash \\\Example: “a string with backslash \\”



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String Constants

#include <stdio.h>int main(void){ printf("%s\n", "a string with double quotes \""); printf("%s\n", "a string with backslash \\"); return 0;}

% gcc string.c% a.outa string with double quotes "a string with backslash \

string.c



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String Constants

Rules: You mustn't split a string constant across

lines (the beginning and ending double quotes must be on the same line).

Two string constants that are separated only by white space are concatenated by the compiler into a single string.



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String Constants

#include <stdio.h>int main(void){ printf("%s\n", "a string with double quotes \""); return 0;}

string1.c

% gcc string1.cstring1.c:4:24: missing terminating " characterstring1.c: In function `main':string1.c:5: error: parse error before "double"string1.c:5: error: stray '\' in programYou mustn't split a string constant across lines (the

beginning and ending double quotes must be on the same line).



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String Constants

Two string constants that are separated only by white space are concatenated by the compiler not a single string.

#include <stdio.h>int main(void){ printf("%s\n", "abc" "def"); return 0;}

string2.c

gcc string2.c% a.outabcdef

What is the output?1. abc2. abc def3. abcdef



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String Constants

Summary String constant is a sequence of characters

enclosed in a pair of double quote marks. String constants are differently form

character constants. Special characters: \”, \\ You mustn't split a string constant across

lines Two string constants that are separated

only by white space are concatenated by the compiler into a single string.



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Outline





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Operators and Punctuators— Outline

Examples of Operators and PunctuatorsPrecedence and Associativity of

OperatorsIncrement and Decrement OperatorsAssignment Operators



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Operators and Punctuators— Examples of Operators and Punctuators

Examples of Arithmetic Operators + addition - subtraction * multiplication / division % modulus

Operators can be used to separate identifiers. a+b

Some symbols have meanings that depend on context

printf(“%d”, b%7);



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Examples of punctuators Parentheses () Braces {} Commas , Semicolons ;

Punctuators also serve to separate language elements.



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Summary Examples of Operators and Punctuators. They are collected by the compiler as

tokens and along with white space, they sever to separate language elements.



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Operators and Punctuators— Precedence and Associativity of Operators

Why Precedence and Associativity? Computers have to be told very precisely

what to do. Precedence and Associativity determine

precisely how expressions are evaluated.



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What is Precedence? A characteristic of operators that indicates

when they will be evaluatedwhen they will be evaluated when they appear in complex expressions.

Operators with high precedence are evaluated before operators with low precedence. Example: 2+3*4 = 14, not 20

You can override precedence rules by using parenthesesparentheses. Example: (2+3)*4 would evaluate to 20.



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What is Associativity? Operators associate with either the expression

on their left or the expression on their right; this is called "associativity."

Associativity rule “left to right”Operations are performed from left to rightExample: +,-,/,%

Associativity rule “right to left”Operations are performed from right to left++(prefix), --(prefix)



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Example: 1+2-3+4-5 Precedence and Associativity Rules:

Precedence: o + and – have the same precedence

Associativity rule: o “left to right”

(((1+2)-3)+4)-5



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Summary Precedence and Associativity determine

precisely how expressions are evaluated. Precedence of operators indicates when they when they

will be evaluatedwill be evaluated. Associativity

“left to right”: Operations are performed from left to right

o Examples: +,-,/,%“right to left”: Operations are performed from right

to lefto Examples: ++(prefix), --(prefix)



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Operators and Punctuators — Increment ++ and Decrement Operators --

SemanticsPrecedence and AssociativityRules



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Increment ++i, i++ Each causes the stored value of i in memory

to be incremented by 1. Each of the expressions has a value.

Example: o a = ++i;

The value of expression ++i is assigned to variable a.

o a = i++; The value of expression i++ is assigned to

variable a.

What is the value of each expression?



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The value of expressions ++i and i++ ++i

the stored value of i is incremented firstthe expression takes as its value the new

stored value of i i++

the expression takes as its value the current stored value of i

the stored value of i is incremented



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#include <stdio.h>int main(void){ int i, j, a, b; i=0; j=0; a = ++i; b = j++; printf("a=%d, b=%d\n",a,b); return 0;}

% gcc id.c% a.outa=1, b=0

id.c



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++ and + ++

Cause the value of a variable in memory to be changed

+Does not change the value of a

variable.



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Decrement Operator i-- and --i The value of i is decremented by 1. Each expression has a value.

--io the stored value of i is decremented by 1o the expression takes as its value the new

stored valued of ii--

o the expression takes as its value the current stored valued of i

o the stored value of i is decremented by 1



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Precedence and Associativity

Associativity ++ (postfix) -- (postfix) Left to right +(unary) –(unary) ++(prefix) --(prefix) Right

to left * / % Left to right + - Left to right



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Precedence and Associativity +(unary) –(unary) ++(prefix) --(prefix) Right to left

#include <stdio.h>int main(void){ int a=2; int result; result = - --a; printf("a=2, - --a = %d\n",result); return 0;}

% gcc id2.c% a.outa=2, - --a = -1

id2.c



Question1: What is the value of a after the operation --a?

Question2: What is the value of the expression --a?

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Examples#include <stdio.h>int main(void){ int a=1, b=2, c=3, d=4; int result1, result2; result1 = ++ a * b - c --; result2 = 7 - - b * ++ d; printf("++ a * b – c -- = %d\n",result1); printf(“ 7 - - b * ++ d = %d\n",result2); return 0;}

++ a * b – c --

++ (postfix) -- (postfix) Left to right+(unary) –(unary) ++(prefix) --(prefix) right to left* / % left to right+ - left to right


)()( )( ++ a * b – 3 2 * b – 3 4 – 3

1

)( )()(id2.c



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Examples#include <stdio.h>int main(void){ int a=1, b=2, c=3, d=4; int result1, result2; result1 = ++ a*b - c --; result2 = 7 - - b * ++ d; printf("++ a * b – c -- = %d\n",result1); printf(“ 7 - - b * ++ d = %d\n",result2); return 0;}

7 - - b * ++ d

++ (postfix) -- (postfix) Left to right+(unary) –(unary) ++(prefix) --(prefix) right to left* / % left to right+ - left to right


7 - (-2) * 5 7 - (-10) 17

)( )(

)(id2.c



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Examples#include <stdio.h>int main(void){ int a=1, b=2, c=3, d=4; int result1, result2; result1 = ++ a*b - c --; result2 = 7 - - b* ++ d; printf("++ a * b – c -- = %d\n",result1); printf(“ 7 - - b* ++ d = %d\n",result2); return 0;}

% gcc id1.c% a.out++ a * b - c -- = 1 7 - - b* ++ d = 17

id2.c



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Rules Applied to variables but not

to constants or ordinary expressions



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Operators and Punctuators— Increment ++ and Decrement Operators --

Examples:

#include <stdio.h>int main(void){ int a, result1, result2; a = 1; result1 = ++1; result2 = -- -a; return 0;}

% gcc id3.cid3.c: In function `main':id3.c:6: error: invalid lvalue in incrementid3.c:7: error: invalid lvalue in decrement

id3.c



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Operators and Punctuators— Increment ++ and Decrement Operators --

Summary ++

++i: the stored value of i is incremented; the expression takes as its value the new stored valued of i

i++: the expression takes as its value the current stored valued of i; the stored value of i is incremented by 1.

-- --i: the stored value of i is decremented by 1; the

expression takes as its value the new stored valued of i i--: the expression takes as its value the current stored

valued of i; the stored value of i is decremented by 1. Applied to variables but not to constants or

ordinary expression



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Operators and Punctuators— Assignment Operators

Example: An assignment expression with = Format: variable = right_side

Two operands o variable o right_side: an expression



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Example: An assignment expression with = Format: variable = right_side Result:

The value of right_side is assigned to variable

Assignment expression has a value.o The value of right_side is the value of the

assignment expression.



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#include <stdio.h>int main(void){ int a, b, c; int a1, b1, c1; b = 2; c = 3; a = b + c; printf("b = %d, c = %d, a = %d \n",b, c, a);

a1=(b1 = 2) + (c1 = 3); printf("b1 = %d, c1 = %d, a1 = %d \n",b1, c1, a1);

return 0;}

% gcc ass1.c% a.outb = 2, c = 3, a = 5b1 = 2, c1 = 3, a1 = 5



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Assignment operators = op=:

+=, -=, *=, / =, %=, >>=, <<=, &=, ^=, |=

Semantics: Variable op= expression

Variable = variable op (expression)



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Assignment operators Precedence:

all the assignment operators have the same precedence

Lower than all the other operators which have been introduced (such as + - )

Associativity:right to left



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#include <stdio.h>int main(void){ int a, b, c; a = b = c = 0; printf("b = %d, c = %d, a = %d \n", b, c, a); return 0;} % gcc ass2.c

% a.outb = 0, c = 0, a = 0



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#include <stdio.h>int main(void){ int i=1, j=2, k=3, m=4; i += j + k; printf(" j = %d, k = %d, i += j+k = %d \n",j, k, i); printf(" m = %d, k = %d, ",m, k); j *= k = m + 5; printf("j *= k = m + 5 = %d \n",j); printf("k = %d \n",k); return 0;}

% gcc ass3.c% a.out j = 2, k = 3, i += j+k = 6 m = 4, k = 3, j *= k = m + 5 = 18 k = 9



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Summary Assignment operators

Precedence: they have the same precedence

o Lower than all the other operators which have been introduced (such as + - )

Associativity: right to left Variable op= expression

Variable = variable op (expression)The value of the expression is the value

of the expression



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Operators and Punctuators— Summary

Examples of Operators and PunctuatorsPrecedence and Associativity of Operators Increment and Decrement Operators

i++, i++ i--, --i

Assignment Operators Variable op= expression

Variable = variable op (expression)The value of the expression is the value of the

expression



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Lexical Elements

Summary Comments Keywords Identifiers Constants String Constants Operators and Punctuators


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Lexical Elements

Comment What is comment?

Arbitrary strings of symbols placed between the delimiters /* and */.

Single line comment: // text The compiler changes each comment into a

single black character. Rules:

Multi-line comments cannot be placed in the middle of a keyword or identifier.

Multi-line comments may not be nested.


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Lexical Elements

Keywords What is Keywords?

Keywords are explicitly reserved words that have a strict meaning as individual tokens in C.

Examples of KeywordsData Type: int, char, long, short

Keywords cannot be redefined or used in other contexts.


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Lexical Elements

Identifiers What is identifier?

The names of variables, functions, labels and other user-defined items are called identifier.

Special identifier Keywords, names of functions in C library,

main Rules:

1. composed of letters, digits, and underscore _ .2. The first character must be a letter or

underscore.3. case-sensitive4. would not be defined as the special identifiers:


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Lexical Element

Constants Integer constants: 0, 17

Decimal integer: 17Octal integer: 017Hexadecimal integer: 0x17An integer may be too large to be stored

in a machine word. Floating constants: 1.0, 3.14 Character constants: (enclosed between single

quotes)



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Lexical Elements

String Constants String constant is a sequence of characters

enclosed in a pair of double quote marks. String constants are differently form

character constants. Special characters: \”, \\ You mustn't split a string constant across

lines Two string constants that are separated

only by white space are concatenated by the compiler not a single string.



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Lexical Elements

Operators and Punctuators Precedence and Associativity of Operators Increment and Decrement Operators

i++, i++i--, --i

Assignment OperatorsVariable op= expression

Variable = variable op (expression)o The value of the expression is the value of the

expression



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Outline





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An Example: Computing Powers of 2— Outline

Program pow_of_2 Dissection of the pow_of_2 Program

CommentsKeywordsIdentifiersConstantsString ConstantsOperators and Punctuators

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An Example: Computing Powers of 2— power_of_2.c

/* Some powers of 2 are printed. */

#include <stdio.h>

int main(void){ int exponent = 0, power_of_two = 1;

while (++exponent <= 10) printf("%5d", power_of_two *= 2); printf("\n"); return 0;}

pow_of_2.c

CommentsKeywordsIdentifiersConstantsString ConstantsOperators and Punctuators

How many times the body of the loop is executed?

power_of_two = power_of_two * 2

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An Example: Computing Powers of 2— power_of_2.c

/* Some powers of 2 are printed. */

#include <stdio.h>

int main(void){ int exponent = 0, power_of_two = 1;

while (++exponent <= 10) printf("%5d", power_of_two *= 2); printf("\n"); return 0;}

% gcc pow_of_2.c% a.out 2 4 8 16 32 64 128 256 512 1024%

Purpose: prints on a line some powers of 2.

pow_of_2.c

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Outline





129

The C System

C is a small language The core language is small Non-essential functionality, such as math functions

or file handling, is provided by a standardized set of library routines.The standard library contains many useful

functions that add considerable power and flexibility to the c System.

What is standard library?How to use a function in standard library?

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The C System— Outline

The Standard library What is standard library? How to use a function in standard library?

#include

An Example: A prn_rand Program

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The C System— The Standard Library

What is Standard library? The C standard library is a collection of

header files and library routines

used to implement common operations, such as input/output and string handling.

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What is Standard library? (Contd.) Header file:

The names and characteristics of functions are included into computer files called header file.

Library file: The actual implementation of functions

are separated into a library file.The library contains compiled code that is

unreadable to humans.

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Examples of header files: <math.h>: For computing common

mathematical functions <stdio.h>: Provides the core input and

output capabilities of the C language. This file includes the venerable printf function.

<stdlib.h>: For performing a variety of operations, including conversion, pseudo-random numbers, memory allocation, process control, environment, signalling, searching, and sorting.

<string.h>: For manipulating several kinds of strings.

Check Appendix A for Details

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How to use a function in the standard library? The programmer needs to provide the

function prototype.Including appropriate header files.

Do we need to locate the function in the library file? No. The system knows where to find the code

that corresponds to functions from the standard library.

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How to use a function in the standard library? Find the header file which contains the

prototype of the function. Use #include preprocessing directive to

include the appropriate file.

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The C System— The Preprocessor: #include

#include “filename” A search for this file is made first in the

current directory and then in other system-dependent places

#include <filename> The preprocessor looks for the file only in

the system-dependent places and not in the current directory.

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The C System— Outline

The Standard library What is standard library? How to use a function in standard library?

#include

An Example: A prn_rand Program

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The C System— An example: prn_rand Program

Purpose of prn_rand program: Use rand() to generate some randomly

distributed integers.

Where is rand()? stdlib.h

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The C System— An example: prn_rand Program/*Printing random numbers. */#include <stdio.h>#include <stdlib.h>int main(void){ int i, n; printf("\n%s\n%s", "Some randomly distributed integers will be printed", "How many do you want to see? "); scanf("%d", &n); for(i=0;i<n;++i){ if (i%6==0) printf("\n"); printf("%9d", rand()); } printf("\n"); return 0;}

Hearder files are included

The characters typed in are received and converted into the format of decimal integeter and placed at the address of n

i=0;while (i++<n){……}

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The C System— An example: prn_rand Program/*Printing random numbers. */#include <stdio.h>#include <stdlib.h>int main(void){ int i, n; printf("\n%s\n%s", "Some randomly distributed integers will be printed", "How many do you want to see? "); scanf("%d", &n); for(i=0;i<n;++i){ if (i%6==0) printf("\n"); printf("%9d", rand()); } printf("\n"); return 0;}

% gcc prn_rand.c% a.out

Some randomly distributed integers will be printedHow many do you want to see? 17

16838 5758 10113 17515 31051 5627 23010 7419 16212 4086 2749 12767 9084 12060 32225 17543 25089%

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The C System— Summary

The Standard library How to use a function in standard library?

#include

The Preprocessor and #includeAn Example: A prn_rand Program

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Outline





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