SysProg-Tutor 01 Introduction to C Programming Language

Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 1

Introduction to C Programming Language

Tutor Session I:

Wongyos Keardsri (P’Bank)Department of Computer EngineeringFaculty of Engineering, Chulalongkorn UniversityBangkok, Thailand

Mobile Phone: 089-5993490E-mail: wongyos@gmail.com, MSN: bankberrer@hotmail.comTwitter: @wongyos

2 2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 1

Tutor Outline

IntroductionC HistoryC Language VS Java LanguageC Language Structure

Types, Operators and ExpressionsData Input and Output

printf()scanf()

Control FlowIf-ElseSwitch

WhileDo-WhileFor

Functions and Program Structure

Non-Return FunctionReturn FunctionThe Standard C Library Functions

Array, Pointer and StringStructuresFile Operations

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C is a structured computer programming languageAppeared in1972 (1970s)Designed and Developed by Dennis Ritchie at the Bell Telephone LaboratoriesDerived from B and BCPL programming languageDeveloped for the UNIX operating system

IntroductionC History

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Used and Implemented for: System programmingOperating systemsEmbedded system applications

C standard: ANSI C and ISO CBook: The C Programming Language, 2nd edition

http://en.wikipedia.org/wiki/C_(programming_language)

IntroductionC History (Cont)

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public class Hello {public static void main(String[] args) {

System.out.print("Hello CP\n");}

Example Java Code (Hello.java)

Example C Code (Hello.c)#include <stdio.h>main() {

printf("Hello CP\n");}

IntroductionC Language VS Java Language

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C: Structured ProgrammingC CompilerEditor: Turbo C, vi, etc.Compile: (UNIX)gcc Hello.c

After compilea.out

Run:./a.outHello CP

Java: Object-Oriented ProgrammingJava Compiler (JVM)Editor: JLab, Eclipse, etc.Compile:javac Hello.java

After compileHello.class

Run:java HelloHello CP Show an exampleShow an example

IntroductionC Language VS Java Language (Cont)

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General format#include <stdio.h>#include <…………………>

main() {

[function-body];

type func() {

[function-body];

Preprocessor / Including Library

Function main:[declaration-list] + [statement-list]

Function func:[declaration-list] + [statement-list]

End... Semicolon

IntroductionC Language Structure

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Introduction

An example C code

#include <stdio.h>main() {

int sum; /* Variable declaration */sum = 15 + 25; /* Value assignment */printf("The sum of 15 and 25 is %d\n", sum);

The sum of 15 and 25 is 40

C Language Structure (Cont)

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Compile C by UNIX command

cc option file1 file2 …

Example 1gcc example.c

./a.out

Compile

IntroductionC Language Structure (Cont)

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Example 2

gcc –c example.c

example.o

gcc –o example.run example.o

Compile

Convert to Executable file

Object file

./example.run

example.run Executable file

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Example 3

gcc –o example.run example.c Compile

./example.run

example.run Executable file

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Types, Operators and Expressions

char Character (8 bit) Ex. ‘A’, ‘a’, ‘F’int Integer (16 bit) Ex. 12, -2456, 99851float Real single (32 bit) Ex. 23.82, 567.008double Real double (64 bit) Ex. 0.0002100009short Shot integer (16 bit) Ex. -4, 18long Long integer (32 bit) Ex. 9547604608456unsigned Unsigned integer (16 bit) Ex. 2, 908, 1392

Data Types and Sizes

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Exampleint x, y, x = 5;float eps = 1.0e-5;int limit = MAXLINE+1;char s_name = 'A';char str[] = "Hello CP";double dd = 0.000000000001;

Variable Declaration

type-specifier list-of-variables;

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Example#define MAX 500#define STEP 20#define PI 3.14159265#define VTAB '\t'const char msg[] = "warning: ";const double e = 2.71828182845905;

Constant Declaration

#define VARIABLE constant-value

#include <stdio.h>#define XX 0

main() {// Body program

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Arithmetic OperatorsAddition +Subtraction -Multiplication *Division /Modulation %

Examplefag = x % y;c = a – (a/b)*b;sum = var1 + var2 + var3;

Expression and Operations

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Relational OperatorsLess than < a < 5Less than or equal <= a <= bMore than > a > b + cMore than or equal >= a >= b + 5Equal == a == -6Not equal != a != 0

Logical OperatorsAND && (a > 0) && (b > 0)OR || (a <= 0) || (b <= 0)Negation ! !(a && c)

Expression and Operations (Cont)

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Bitwise OperatorsBitwise AND &Bitwise OR (Inclusive OR) |Bitwise XOR (Exclusive OR) ^Left shift <<Right shift >>One's complement ~

Examplex = 01001011 y = 00101100 ~x = 10110100x & y = 00001000 x | y = 01101111x ^ y = 01100111 x << 2 = 00101100

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Assignment Operators and Expressionsop is + - * / % << >> & ^ |If expr1 and expr2 are expressions, then

expr1 op= expr2

Equivalent to

expr1 = (expr1) op (expr2)

ExampleX += 1;X = X + 1;

Equivalent

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Conditional Expressions

expr1 ? expr2 : expr3

If expr1 is true do expr2If expr1 is false do expr3

Examplea = 5;b = 10;min = (a < b) ? a : b;

Types, Operators and ExpressionsExpression and Operations (Cont)

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Increment and Decrement OperatorsPre-increment operation ++variablePost-increment operation variable++Pre-decrement operation --variablePost-decrement operation variable--

Examplex = 4;y = x++ + 5; //x = 5, y = 9x = 4;y = ++x + 5; //x = 5, y = 10

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Type Cast Operator (Casting)

(type-specifier) expression;

Example(double) date;float var1 = 2.7;int var2 = (int) var1; //var2 = 2(char) x;(int) d1 + d2;

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Data Input and Output

printf() is a function for display result to standard output (Monitor, Screen)

printf(format, arg1, arg2, …);

Exampleprintf(“Hello\n”);//Helloint num = 2;printf(“%d is integer”, num);//2 is integer

printf() Statement

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Conversion Operation [printf()]d signed decimal conversion of an int or a longu unsigned decimal conversion of unsignedo unsigned octal conversion of unsignedx, X unsigned hexadecimal conversion of unsigned

x = [a – f], X = [A - F]c single character conversions string conversionf signed decimal floating point conversione, E signed decimal floating point conversion in scientific

notation

Data Input and Outputprintf() Statement (Cont)

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int j = 45, k = -123;float x = 12.34;char c = ‘w’;char *m = “Hello”;printf(“Hello 55”); Hello 55printf(“Tax is %d”, j); Tax is 45printf(“%d”, j+k); -78printf(“%3d %d”, j, k); 45 -123printf(“%f %.2f”, x, x); 12.340000 12.34printf(“%c”, c); wprintf(“%s\n”, m); Helloprintf(“%s\n”, “Hello”); Helloprintf(“%10s\n”, “Hello”); Hello

Example of printf()

Result

Data Input and Outputprintf() Statement (Cont)

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scanf() is a function for read input from standard input (Keyboard)

scanf(format, arg1, arg2, …);

Examplescanf(“%d %d %d”, &day, &month, &year);int num;printf(“Enter integer : ”);scanf(“%d”, &num);// Enter integer : 23

Data Input and Outputscanf() Statement

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Conversion Operation [scanf()]d signed decimal conversion of an int or a longu unsigned decimal conversion of unsignedo unsigned octal conversion of unsignedx, X unsigned hexadecimal conversion of unsigned

x = [a – f], X = [A - F]c single character conversions string conversionf signed decimal floating point conversione, E signed decimal floating point conversion in scientific

notation[] read only character in [ ], if [^ ] read different character

Data Input and Outputscanf() Statement (Cont)

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int d,m,y,x;char ch1,ch2;float f;scanf(“%d”, &x); 4

// x=4scanf(“%2d%2d%4d”, &d,&m,&y); 22062007

// d=22, m=6, y=2007scanf(“%d/%d/%d”, &d,&m,&y); 22/06/2007

// d=22, m=6, y=2007scanf(“%c%c”, &ch1,&ch2); Ab

// ch1=‘A’, ch2=‘b’scanf(“%f”, &f); 2.3

// f=2.300000

Example of scanf()

Result

Data Input and Outputscanf() Statement (Cont)

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Control Flow

If-Else StatementThe if-else statement is used to express decisions. Formally the syntax is

if (expression) {true statement

} else {false statement

Decision Statements

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Control Flow

Nested If-ElseThe sequence of if statements is the most general way of writing a multi-way decision. Formally the syntax is

if (expression) {statement

} else if (expression) {statement

} else {statement

Decision Statements (Cont)

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Control Flow

Example of If-ElseDecision Statements (Cont)

if (score >= 80)grade = ‘A’;

else if (score >= 70)grade = ‘B’;

else if (score >= 50)grade = ‘C’;

else if (score >= 40)grade = ‘D’;

elsegrade = ‘F’;

if (a < b) {printf(“a less than

b\n”);} else {

temp = a;a = b; /* swap a */b = temp; /* and b */printf(“Interchange a

and b\n”);}

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Control Flow

Switch StatementThe switch statement is a multi-way decision that tests whether an expression matches one of a number of constant integer values, and branches accordingly.

switch (expression) {case const-expr: statementscase const-expr: statementsdefault: statements

Decision Statements (Cont)

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Control Flow

Example of SwitchDecision Statements (Cont)

c = getchar();switch (c) {

case '0': printf(“Zero\n”); break;case '1': case '2': case '3': case '4':case '5': case '6': case '7': case '8':case '9': printf(“Nine\n”); break;case ' ':case '\n': newln++; break;case '\t': tabs++; break;default: printf(“missing char\n”); break;

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Control Flow

While StatementThe expression is evaluated. If it is true, statement is executed and expression is reevaluated. This cycle continues until expression becomes false.

while (expression) {Statement1;Statement2;...

Iteration Statements

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Control Flow

Example of While

#include <stdio.h>#define DOT ‘.’main() {

char C;while ((C = getchar())!= DOT)

putchar(C);printf(“Good Bye.\n”);

Result?

Iteration Statements (Cont)

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Control Flow

Do-While StatementThe do-while, tests at the bottom after making each pass through the loop body; the body is always executed at least once.

do {statement1;statement2;…

} while (expression);

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Control Flow

Example of Do-While

int i = 1, sum = 0;do {

sum += i;i++;

} while (i <= 50);printf(“The sum of 1 to 50 is %d\n”, sum);

Result?

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Control Flow

For StatementThe for statement

for (initial; expression; update) {statement;

Equivalent to

initial;while (expression) {

statement;update;

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Control Flow

Example of Forfor (i=1;i<=100;i++) {

x += i;if ((x % i) == 0) { i--; }

for (i=0, j=strlen(s)-1; i<j; i++,j--){ c = s[i], s[i] = s[j], s[j] = c; }

char c;int count;for (count=0; (c=getchar() != ‘.’); count++)

{ }printf(“Number of characters is %d\n”, count);

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Control Flow

Break and Continue StatementThe break statement provides an early exit from for, while, and do-while.

break;

The continue statement is related to break, but less often used; it causes the next iteration of the enclosing for, while, or do-while loop to begin.

continue;

Sequential Statements

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Control Flow

Example of Break and Continue

int c;while ((c = getchar()) != -1) {

if (C == ‘.’)break;

else if (c >= ‘0’ && c <= ‘9’)continue;

else putchar(c);}printf(“*** Good Bye ***\n”);

Sequential Statements (Cont)

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Functions (Method in Java) break large computing tasks into smaller ones, and enable people to build on what others have done instead of starting over from scratch.

function-name (argument declarations) {[ declaration-list][ statement-list ]

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Example of Function

(Cont)

/* Programming in function */main() {

int hours, minutes, seconds;int total_time = 0;int convert(); printf(“Enter time in hours-minutes-seconds : “);scanf(“%d %d %d”, &hours, &minutes, &seconds);total_time = convert(hours, minutes, seconds);

/* calling point */printf(“The converted time is %d seconds\n”,

total_time);}

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Example of Function (Cont)

(Cont)

/* Function (called function) */int convert (h, m, s)int h, m, s;{

int time; /* return-value variable */time = (60 * h + m) * 60 + s;return time; /* exiting point */

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Example of Non-Return Function

Non-Return Function

/* Main */main() {

void display();display();

/* Function Part */void display() {

printf(“*** Hello and Good bye ***”);}

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Example of Return Function

Return Function

/* Main Function */main() {

float sq,x;float square();sq = square(x);printf(“The square of x is %f\n”, sq);

/* Function: square */float square(x) {

return(x * x);}

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Example of External Variable

External Variable

main() {int k = 15;func1();func2();printf(“k = %d\n”, k);

int k = 5; /* External Variable */

func1() { printf(“k = %d\n”, k); } /*Function 1*/func2() { printf(“k = %d\n”, k); } /*Function 2*/

k = 5k = 5k = 15

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Example of Recursive Function

Recursive Function

main() { /* Main Part */int j;long int factorial();for (j = 0; j <= 10; j++)

printf(“%2d! is %ld\n”, j, factorial(j));}

long int factorial(n) /* Function Part */int n;{ if (n == 0) return (1);

else return (n * factorial(n-1));}

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#include <stdio.h>

clearerrfclosefeofferrorfflushfgetcfgetsfopen

fprintffputcfputsFreadfreopenfscanffseekftell

fwritegetcgetchargetsprintfputcputcharputs

rewindscanfsprintfsscanfungetc

The Standard C Library Functions

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#include <math.h>

acos(x)asin(x)atan(x)ceil(x)cos(x)cosh(x)exp(x)fabs(x)

floor(x)log(x)log10(x)sin(x)sinh(x)sqrt(x)tan(x)tanh(x)

atan2(x,y)power(x,y)

The Standard C Library Functions (Cont)

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#include <ctype.h>

The Standard C Library Functions (Cont)

isalnumisalphaisasciiiscntrlisdigitisgraphislowerisprint

ispunctisspaceisuppertolowertoupper

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Array, Pointer and String

Array is a group of related data items. In C, there is a strong relationship between pointers and arrays, strong enough that pointers and arrays should be discussed simultaneously.The declaration of one-dimensional array

type array-name[number-of-elements];

int a[15];

a[0], a[1], a[2], … , a[14] = 15 Element

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In the main memory

Array (Cont)

a a[0] 5501a[1] 5502a[2] 5503

… …… …… …

a[14] 5514

Value Address

int a[15];

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Example of Array

Array (Cont)

/* Read five integers from the standard input and display them in reverse order */

#define MAX 5main() {

int j;int a[MAX];

for (j = 0; j < MAX; j++)scanf(“%d”, &a[j]);

for (j = MAX - 1; j >= 0; j--)printf(“%d\n”, a[j]);

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A pointer is a variable that contains the address of a variable.Example of pointer

Pointer

Value Address

x 25 7960

px 8132

px = &x

int x = 25;int *px;px = &x;int y = *px;//y = x = 25

x = 25

y = *pxy

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Example (Cont)Pointer (Cont)

main() {int x = 5, *px;px = &x;int y = *px;printf("x = %d\n", x);printf("y = %d\n", y);printf("*px = %d\n", *px);printf("&x = %d\n", &x);printf("px = %d\n", px);printf("&y = %d\n", &y);x = 34;printf("px = %d\n", px);printf("*px = %d\n", *px);printf("y = %d\n", y);

x = 5y = 5*px = 5&x = -4195036px = -4195036&y = -4195044

px = -4195036*px = 34y = 5

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Example

Pointer (Cont)

main() {int t[10];int *pt;for (pt = t; pt < &t[10]; pt++)

scanf(“%d”, pt);for (pt = &t[10]; pt >= t; pt--)

printf(“%d\n”, *pt);}

int x;int *px, *py;px = &x;py = px;

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Example (Cont)

Pointer (Cont)

int x = 1, y = 2, z[10];int *ip; /* ip is a pointer to int */ip = &x; /* ip now points to x */y = *ip; /* y is now 1 */*ip = 0; /* x is now 0 */ip = &z[0]; /* ip now points to z[0] */

Help me!!

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A string constant, written as "I am a string" is an array of characters. In the internal representation, the array is terminated with the null character '\0'so that programs can find the end.Example

String

char amessage[] = "now is the time";/* an array */char *pmessage = "now is the time";/* a pointer */

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Example of String

String (Cont)

char s1[] = “xyz”;char s2[] = {‘x’, ‘y’, ‘z’, ‘\0’};char *s3 = “xyz”;

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Example/* COUNT THE LENGTH OF STRING */main() {

char *w = “good morning”;int len();printf(“Lengths of string is %d\n”, len(w));

/* FUNCTION: len() for counting the length of string */int len(string)char string[]; // char *string;{

int count = 0;while (string[count] != NULL) count++;return (count);

String (Cont)

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Structures

A structure is a collection of one or more variables, possibly of different types, grouped together under a single name for convenient handling.Structures are called "records'' insome languages, notably Pascal.

struct structure-name { type-specifier variable;...

Members

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Structures

Example of Structure(Cont)

struct person {int code;char name[30];char address[40];float salary;

struct point {int x;int y;

int x int y

int code

string name

string address

float salary

Record = Node

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Structures

A struct declaration defines a type.

struct structure-name variable-name,…;

Or declare in

struct structure-name { type-specifier variable;...

}variable-name;

(Cont)

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Structures

Example of Structure Declaration

(Cont)

struct person {int code;char name[30];char address[40];float salary;

};struct person p;

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Structures

A member of a particular structure is referred to in an expression by a construction of the form

struct-variable-name.member-name

Examplep.code;p.name;p.address;p.salary;

(Cont)

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Structures

Example of Struct Program(Cont)

/* ASSIGN AND PRINT A DATE */main() {

struct date {int dd = 22;int mm;int yyyy;

};struct date today;today.mm = 6;today.yyyy = 2007;printf(“Date is %2d/%2d/%4d\n”, today.dd,

today.mm, today.yyyy);}

//ResultDate is 22/ 6/2007

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File Operations

The input and output functions, types, and macros defined in <stdio.h> represent nearly one third of the library.The following functions deal with operations on files:

fopen(filename, mode);fclose(file pointer);feof(file pointer);getc();putc();

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File Operations

fopen() - opens the named file, and returns a stream, or NULL if the attempt fails. Legal values for mode include:

"r" open text file for reading"w" create text file for writing; discard previous contents if

any"a" append; open or create text file for writing at end of file"r+" open text file for update (reading and writing)"w+" create text file for update, discard previous contents if

any"a+" append; open or create text file for update, writing at

(Cont)

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File Operations

Example of fopen() to open file

(Cont)

FILE *file;FILE *fopen();

if ((file = fopen(“person.dat”, “r”)) == NULL)printf(“Cannot open a data file\n”);

else...

File Pointer

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File Operations

fclose() – close file, flushes any unwritten data for stream, discards any unread buffered input, frees any automatically allocated buffer, then closes the stream. It returns EOF if any errors occurred, and zero otherwise.Example

(Cont)

int fclose();...if (fclose(file) != EOF)

printf(“Cannot close file\n”;else printf(“Now file is closed\n”);

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File Operations

feof() – check for end of file.

getc() is equivalent to fgetc except that if it is a macro, it may evaluate stream more than once.

int getc(file pointer);

putc() is equivalent to fputc except that if it is a macro, it may evaluate stream more than once.

int putc(char c, file pointer);

putchar(c) is equivalent to putc(c,stdout).int putchar(char c);

(Cont)

if (!feof(file))printf(“It is not the end of file now\n”);

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File Operations

fprintf() converts and writes output to stream under the control of format. The return value is the number of characters written, or negative if an error occurred.

int fprintf(file pointer, format, ...)

fscanf() reads from stream under control of format, and assigns converted values through subsequent arguments, each of which must be a pointer.

int fscanf(file pointer, format, ...)

(Cont)

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Example of File Operations Program

File Operations(Cont)

/* A PROGRAM TO WRITE ONE LINE TO sample.txt */#include <stdio.h>main() {

FILE *fp;char c = ‘ ‘;fp = fopen(“sample.txt”, “w”);printf(“Enter text below\n”);while (c != ‘\n’) {

c = getchar();putc(c, fp);

}fclose(fp);

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Example of File Operations Program (Cont)

File Operations(Cont)

/* A PROGRAM TO READ TEXT FROM sample.txt AND DISPLAY ON A MONITOR */#include <stdio.h>main() {

FILE *fp;char c;fp = fopen(“sample.txt”, “r”);if (fp == NULL)

printf(“The file cannot be opened\n”);else

while ((c = getc(fp) != EOF) putchar(c);fclose(fp);

Tutor Session - 1

Question ?

… Answer

SysProg-Tutor 01 Introduction to C Programming Language

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