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ESc101: Fundamentals of Com utin

2011-12-Monsoon Semester

Lecture #25, September 29, 2011

Please switch off your mobile phones.

Announcements

Last date for course dro is 20th October.

I will sign drop requests till 17th October.

Friday Lab Section please note Lab on 14th suspended due to Gymkhana Holiday for Antaragni

It will be conducted on 18th (Tuesday)

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anyone rom r ay a sec ons as a c ass a u or a on

Tuesday afternoon, please let us know by 10th morning.

Tuesday Lab Section please note

10th lab on Saturday, 22nd October, instead of 25th October.

1Dheeraj Sanghi, CSE Dept., IIT Kanpur

ESc101, 2011-12-Monsoon

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Best Programmers for Lab 6

Section Name Section Name

E1 Utkarsh Sanjay Patange E2 Jayant

E3 Unnat Jain E4 Arihant Kumar Jain

E5 Pratik Pradyot Rath E6 Saurav Narang

E7 Mohit Sharma E8 none

E9 Dhrupal R Shah E10 Gagan Agrawal

E11 Swapnil Shwetank Jha E12 Chaitanya Ahuja

E13 Sarthak Sagar E14 Abhishek Verma

E15 Aditya Aggarwal

Lec-25 Dheeraj Sanghi, CSE Dept., IIT Kanpur


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Recap

Structures

members

functions returning structures

passing structures to functions pointers to structures

nested structures

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pointer in a structure

3Dheeraj Sanghi, CSE Dept., IIT Kanpur


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Recap: Structure operations 1

#include

#include

struct point {

double y;

}; // defining a structure

struct point new_point (double c, double d) // structure as return value

{ struct point p;

p.x = c;

p.y = d;

}

double distance (struct point a, struct point b) // structure as parameter

{ return (sqrt (pow (a.x b.x, 2) + pow (a.y b.y), 2));

}



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void modify_wrong (struct point p, double c, double d)

{ p.x = c;

p.y = d;

} // modifications are temporary

vo mo y_r ght (struct po nt p, ouble c, ouble

{ p->x = c;

p->y = d;

} // modifications are permanentint main ( )

{ struct point p, q, s; // declaring structure variables

struct point t = {9.0, -5.0}; // initialization during declaration

double d;

struct point *ptr;

printf(%lf %lf\n, t.x, t.y); // Accessing individual members

q.x = 4.0; // modifying members in structure notation

q.y = -3.0;



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p = new_point (7.0, -1.0); // Setting structure through functions return value

d = distance (p, q); // passing structures as parameters

printf(Distance = %lf\n, d);

// s = {6.0, 2.0}; // error

modify_wrong (p, 12.0, 8.0);

printf(%lf %lf\n, p.x, p.y); // No modification would have happened

ptr = &p;

modify_right (ptr, 12.0, 8.0); // Now p would have been modified

printf(%lf %lf %lf %lf\n, p.x, p.y, ptr->x, ptr->y);

// if (q == p) // error

}



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Recap: Nested structures

A structure can have another structure as its member

struct line {

struct point p;

struct point q;

};

struct line l;

Value x of point p of variable l of type struct line can be

accessed as:

l.p.x

The . operator has left-to-right associativity



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Recap: Array of structures

struct point t [3];

An individual structure is accessed as t[0], etc.

A member of a structure is accessed as t[1].x, etc.

All operations allowed on normal arrays are allowed on

arrays of structures

Just like any other array, it is equivalent to a pointer tostructure



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Recap: Pointer in a structure

A structure can have a pointer as its member

struct student {

int roll;

char *name;

};

struct student s;

Declaring a variable of type struct student just declares the pointer

name it does not allocate space for it

strc (s.name Sudhir // wron

Memory for name has to be allocated explicitly using malloc

s.name = (char *) malloc (30 * sizeof(char));

strcpy (s.name, Sudhir); // right



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Modular programming

Write functions to solve each small part

If your code is more than what you can see in one screen,

then perhaps it is better to divide this into functions



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Example: Nested Structure

struct date {

int day;

int month;

struct student {

int roll;

char *name;

int year;

};

struct marks {int lab;

int quiz;

int midsem;

int hostel;

int room;

long mobile;struct date bday;

struct marks esc101;

struct marks phy;

int labexam;

int final;

int total;

};

}



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Comparing two structures

int stucompareless (struct student s1, struct student s2)

// sort on total marks, then age, and then roll number.

{

if(s1.esc101.total < s2.esc101.total) return 1;

if(s1.esc101.total > s2.esc101.total) return 0;

if(s1.bday.year < s2.bday.year) return 1;

if(s1.bday.year > s2.bday.year) return 0;

if(s1.bday.month < s2.bday.month) return 1;

if(s1.bday.month > s2.bday.month) return 0;

if(s1.bday.day < s2.bday.day) return 1;

if(s1.bda .da > s2.bda .da return 0;

if(s1.roll < s2.roll) return 1;

return 0;

}



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Swapping two student records

void swapstudents (struct student *s1, struct student *s2)

// Notice the arguments are pointers for permanent effect

{

temp = *s1;

*s1 = *s2;

*s2 = temp;

}



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Sorting student records

struct student slist[100];

void sortstudents ( int n) // n records to be sorted

{ // Using Bubblesort will do sorting later

int i, k, swap;

for (k = n; k > 1; k--)

{ swap = 0;

for (i = 0; i < k; i++)

// In each iteration, shift the bigger value record to the right

ifstucompareless (slist[i], slist[i+1])

{ swapstudents (&slist[i], &slist[i+1]);

swap = 1;}

if(!swap) break;

}

}



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Searching student records

struct student slist[100];

int findstudent (struct student s1, int n) // n records to be searched

{ int i;

for (i = 0; i < n; i++) // Linear search

{

if(s1.roll == slist[i].roll) return i

}

return (-1);

}



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Print student record

void printstudent (struct student s)

{

printf(%d\t%s\t%2d %2d %4d\t%ld\n, s.roll, s.name, s.bday.day,

. . , . . , .

printf(Marks in ESc101\n);

printf(Lab: \t\t%d\n, s.esc101.lab);

printf(Quizzes: \t%d\n, s.esc101.quiz);

printf(Mid-sem exam: \t%d\n, s.esc101.midsem);

printf(Lab-exam: \t%d\n, s.esc101.labexam);

printf(End-sem exam: \t%d\n, s.esc101.final);

, . .

}



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Wishing all of you a very

happy Dussehra

En o our vacations

Lec-25 17Dheeraj Sanghi, CSE Dept., IIT Kanpur


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