tutorial & laboratory

PDS Tut. & Lab.: X (CS 11001/19001): Section 1 Dept. of CS&Engg., IIT Kharagpur 1'

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Tutorial & Laboratory

�� Programming & Data Structure: CS11001/19001

��

��Section - 1/A

DO NOT POWER ON THE MACHINE

Department of Computer Science and Engineering

I.I.T. Kharagpur

Spring Semester: 2009 - 2010 (24.03.2010)


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Download

Download the file date240310.ps from

Programming & Data Structures ... of

http://www.facweb.iitkgp.ernet.in/∼goutam

View the file using the command kghostview & orggv &


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Laboratory Test II: 7th April, 2010

• Lab. Test I + 1-D array, recursive function,

string, 2-D array, basic structure.

• Do not carry any book or note book.

• Time: Two hours.

• Marks: 35�� The test will start after the tutorial.


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Quick Sort Algorithm (ascending order)

Let there there be n data elements stored in an

1-D array, a[l · · · h].

1. If l = h(n = 1), it is already sorted!

2. If n > 1,

(a) Partition the data at index m in the array

in such a way that each data in the part

a[l · · · m] is less than or equal to each

data in the part a[m+1 · · · h].


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(b) Sort a[l · · · m] and a[m+1 · · · h]

recursively.

After the partition there will be no datamovement from one part to the other.


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Partitioning the Data

1. Select a data element p as the pivot element.

For a simple implementation we may choose

a[l] as the pivot.

2. Transfer all the elements that are less than

p, to the lower index side of the array and

also transfer elements greater than or equal

to p, to the higher index side.


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Partition Algorithm (non-descending order)

partition(a, l, h)

p ← a[l]

i ← l − 1

j ← h + 1

while true

do j ← j − 1 while a[j] > p

do i ← i + 1 while a[j] < p

if i < j exchange(a[i], a[j])

else return j


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Quick Sort Algorithm

quickSort(a, l, h)

if (l < h)

p ← partition(a, l, h)

quicksort(a, l, p)

quicksort(a, p+1, h)


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Quick Sort : An Example


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# #

0 1 2 3 4 5 6 7

# #

# #

0 1 2 3 4 5 6 7

# #

# #

0 1 2 3 4 5 6 7

# #

Call 0

x

p

x

x

21 3 9 11 5 9

3 9 11 5 9

9 11 5

Unsorted Array

1339

21

9

39 13

21

i=−18

j=8

j=7

j=7

3

x[i] <−−> x[j]

3913 21

i=0


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# #

0 1 2 3 4 5 6 7

# #

x

11 5

p93 9

j=7

2113 39 21

i=0

# #

0 1 2 3 4 5 6 7

# #

x

5 913 3 21939 11

i=6

# #

0 1 2 3 4 5 6 7

# #

x x[i] <−−> x[j]

13 3 9 11 5 21

i=6i=2

9 39


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# #

0 1 2 3 4 5 6 7

# #

x

p2113 2151193

j=6j=2

# #

0 1 2 3 4 5 6 7

# #

x

p2113 2151193

9 39

9 39

j=5

# #

0 1 2 3 4 6 7

# #

x

39

5

partition index

3 9 115913 21

No data crossing

i=6


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Dynamic Allocation of 1-D Array


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Request for Run-Time Memory Allocation

• The volume of data may not be known

before the run-time.

• It provides flexibility in building data

structures.

• The space is allocated in global data area

(not on the stack) called heap.


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void *malloc(size t n)

The C library function malloc() is used torequest for an allocation of n bytes ofcontiguous memory space in the global dataarea. After a successful allocation the functionreturns a generic pointer void * that can becasted to any required type.


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void *malloc(size t n)

If malloc() fails to allocate the requestedspace, it returns a NULL pointer. The interfaceof the function is defined in the header filestdlib.h, so it is to be included.


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1-D Array of n Elements

We can use a variable of type int * and a callto malloc() to create an 1-D array of nelements of type int, where n is an input data.


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Dynamic 1-D Array

#include <stdio.h>

#include <stdlib.h>

int main()

{

int *p, n, i, val = 1 ;

printf("Enter a +ve integer: ");

scanf("%d", &n);

p = (int *)malloc(n*sizeof(int));

for(i=0; i<n; ++i) {

p[i] = val; val = 2*val;

}


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for(i=0; i<n; ++i) printf("%d ",p[i]);

putchar(’\n’);

return 0;

} // dynamic1D.c


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Student’s Data

Let us consider data related to every student ofa college (say IIT). There may be a largenumber of data items, but for simplicity weonly consider the name, roll number, sgpa andgrade points in different semesters, and thecgpa upto the last semester. The correspondingproduct data type or the structure in C maylook like the following one.


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Student Data

#define NAME 50#define ROLL 9struct sgpa {

float sgpa;int gp;

};typedef struct {

char name[NAME], roll[ROLL] ;int sem ;struct sgpa sgpa[10];float cgpa ;

} student;


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Assignment XII

The student data is available in a data file(stdData). Write a C program to readstudent-data in a dynamically created array oftype student, from the stdin (keyboard). Thedata will be redirected from the data file.


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student *sP

sp = (student *)malloc(n*sizeof(student));

sP 012

n−1

semname[50]

roll[9] sgpa[10]

cgpa


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Assignment XII

The program computes the cgpa upto the lastsemester for each student and stores it in thecorresponding cgpa field. It sorts the studentrecords (indirectly) to prepare a merit list(non-ascending order on the cgpa) using thequick-sort algorithm. Finally it prints thesorted list of students along with their rollnumbers and cgpas.


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Input Data: stdData

70

08CE1012 Sukesh Jain 3 20 8.5 25 8.0

08CS1020 Ansuman Roy 3 22 8.0 23 7.5

08PH1010 Ruma Ahamed 3 25 9.0 20 8.5

.................

08EE1007 Simranjit S Mann 3 23 8.5 22 8.5

08EC1023 P V Verma 3 20 8.0 25 9.0

08CH1016 P V Tiwari 3 20 8.0 25 9.0


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Different Functions

The functionstudent *readStudent(int *nsP);reads the number of students and updates thelocation *nsP (in the caller), creates an array oftype student of size n; reads in each element ofthe array, the roll number, name, currentsemester number and (credit point, sgpa) pairsupto the last semester. Finally it returns thestarting address of the array.


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Reading Roll No. & Name

�� scanf("%s %[∧0-9]%d", ...


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Different Functions

The functionvoid calcCgpa(student *sP, int n);takes the starting address of the student arrayand the number of students as parameters andcomputes the cgpa of each student and stores itin the cgpa field of each record in the array.


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cgpa Calculation

If the number of the current semester is sem

then

cgpa =

sem−2∑

i=0

gpi × sgpai

sem−2∑

i=0

gpi

.


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Different Functions

The functionint *initIndex(int n);takes the number of students n as parameter,dynamically creates an n-element array of typeint, initializes the ith location of the array to i,the initial index of the ith student in thestudent array.


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1

19

1

19

sP

indP0

0

19

10

08CE1012 Sukesh Jain ******08CS1020 Ansuman Roy *****

08SI2024 Sagar Jyoti *******


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Different Functions

The functionvoid writeStudent(student sP[], intindP[], int n);takes the starting address of the student array,the starting address of the index array and thenumber of students as parameters. It prints thestudents array following the sequence of theindex array i.e. the index of the student record(in the array) printed in the ith line, is stored inindP[i].


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Different Functions

The functionvoid quickSort(student sP[], intindP[], int low, int high);takes four parameters. The last two parametersare the low and the high indices of indP[]within which data in sP[] are to be sortedindirectly in non-ascending order.


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Unsorted Data

1 1

sP

indP0

01

008CS1020 Ansuman Roy

2345

76

234567

234567

7.4808CH3017 Manoj Meena 6.82

08NA1002 Karan Rao 7.828.3608CH1016 N Prasad

8.1408PH1010 Rusha Ahamed6.4708SI2024 Sargar Jyoti

08GG2010 Anant Raju

08CE1012 Sukesh Jain

7.82

8.41


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Sorted Data

1

sP

indP0

01 08CS1020 Ansuman Roy

2345

76

234567

7.4808CH3017 Manoj Meena 6.82

08NA1002 Karan Rao 7.828.3608CH1016 N Prasad

8.1408PH1010 Rusha Ahamed6.4708SI2024 Sargar Jyoti

08CE1012 Sukesh Jain 8.41

7.8208GG2010 Anant Raju

37506124 Student Array Unchanged

Sorted Sequence indicesin the Index Array


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Different Functions

The functionstatic int partition(student sP[], intindP[], int low, int high);the index array indP[] is partitioned on thecgpa values of the sP[] array (in non-ascendingorder). But the order of data in sP[] areunchanged. The key-word static indicatesthat the function is local to the file.


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Input Data and Report

Test your program with the data in the filestdData. After you are satisfied, send the .cfile.$ ./a.out < stdData

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