Structure and Functions

STRUCTURES AND FUNCTIONS

For structures to be fully useful, we must have a mechanism to pass them to functions and return them. A function may access the members of a structure in three ways as shown in Figure 8.4.

 Passing Individual Members

To pass any individual member of the structure to a function we must use the direct selection operator to refer to the individual members for the actual parameters. The called program does not know if the two variables are ordinary variables or structure members. Look at the following code that illustrates this concept.

#include <stdio.h>

typedef struct

{

int x;

int y;

}POINT;

void display (int, int);

int main()

{

POINT p1 = {2, 3};

display (p1.x, p1.y);

return 0;

}

void display (int a, int b)

printf("The coordinates of the point are: %d %d", a, b);

Output

The coordinates of the point are: 2 3

Passing the Entire Structure

Just like any other variable, we can pass an entire structure as a function argument. When a structure is passed as an argument, it is passed using the call by value method, i.e., a copy of each member of the structure is made. This is a very inefficient method especially when the structure is very big or the function is called frequently. In such a situation passing and working with pointers may be more efficient.

The general syntax for passing a structure to a function and returning a structure can be given as de SMIT

struct struct_name func_name (struct struct_ name struct_var);

This syntax can vary as per need. For example, in some situations we may want a function to receive a structure but return a void or value of some other data type. The following code passes a structure to the function using the call-by-value method.

#include <stdio.h>

typedef struct

{

int x;

int y;

}POINT;

void display (POINT);

main ()

{

POINT p1 = {2, 3};

display (p1);

return 0;

}

void display (POINT p)

{

printf("%d %d", p.x, p.y);

}

8. Write a program to read, display, add, and subtract two distances.  Distance must be defined using kms and metres.

#include <stdio.h>

#include <conio.h>

typedef struct distance

{

int kms;

int metres;

}DISTANCE;

DISTANCE add_distance (DISTANCE, DISTANCE);

DISTANCE subtract_distance (DISTANCE,

DISTANCE);

DISTANCE d1, d2, d3, d4;

int main()

{

int option;

clrscr();

do

printf("\n ***** MAIN MENU *****");

printf("\n 1. Read the distances ");

printf("\n 2. Display the distances");

printf("\n 3. Add the distances");

printf("\n 4. Subtract the distances");

printf("\n 5. EXIT");

printf("\n Enter your option: ");

scanf("%d", &option);

switch (option)

{

case 1:

printf("\n Enter the first distance in kms and metres: ");

scanf("%d %d", &d1.kms, &d1. metres);

printf("\n Enter the second distance in kms and metres: ");

scanf("%d %d", &d2. kms, &d2. metres);

break;

case 2:

printf("\n The first distance is: %d kms %d metres", d1.kms, d1. metres);

printf("\n The second distance is: %d kms %d metres", d2.kms, d2. metres);

break;

case 3:

d3 = add_distance (d1, d2);

printf("\n The sum of two distances is: %d kms %d metres", d3.kms, d3.metres);

break;

case 4:

d4 = subtract distance (d1, d2);

printf("\n The difference between two distances is: %d kms %d metres", d4. kms, d4.metres);

break;

}

}while (option != 5);

getch();

return 0;

}

DISTANCE add_distance (DISTANCE d1, DISTANCE d2)

{

DISTANCE sum;

sum.metres = d1.metres + d2. metres;

sum.kms d1.kms + d2.kms;

if (sum.metres >= 1000)

{

sum.metres = sum.metres%1000;

sum.kms += 1;

}

return sum;

}

DISTANCE subtract_distance (DISTANCE d1, DISTANCE d2)

{

DISTANCE sub;

if (d1.kms > d2.kms)

{

sub.metres = d1.metres - d2. metres;

sub.kms = d1.kms d2. kms;

}

else

{       

sub.metres = d2.metres – d1. metres;

sub.kms = d2.kms - d1.kms;

}

if (sub.metres < 0)

{

sub.kms = sub.kms - 1;

sub.metres = sub.metres + 1000;

}

return sub;

}

Output

***** MAIN MENU *****

1. Read the distances

2. Display the distances

3. Add the distances

4. Subtract the distances

5. EXIT

Enter your option: 1

Enter the first distance in kms and metres: 5 300

Enter the second distance in kms and metres: 3 400

***** MAIN MENU *****

1. Read the distances

2. Display the distances

3. Add the distances

4. Subtract the distances

5. EXIT

Enter your option: 3

The sum of two distances is: 8 kms 700 metres

9. Write a program to read, display, add, and subtract two time variables defined using hours, minutes, and seconds.

#include <stdio.h>

#include <conio.h>

typedef struct

{

int hr;

int min;

int sec;

}TIME;

TIME t1, t2, t3, t4;

TIME subtract_time (TIME, TIME);

TIME add_time (TIME, TIME);

int main()

{

int option;

clrscr();

do

{

printf("\n **** MAIN MENU ****");

printf("\n 1. Read time ");

printf("\n 2. Display time");

printf("\n 3. Add");

printf("\n 4. Subtract");

printf("\n 5. EXIT");

printf("\n Enter your option: ");

scanf("%d", &option);

switch (option)

{

case 1:

printf("\n Enter the first time in hrs, mins, and secs: ");

scanf("%d %d %d", &t1.hr, &t1.min, &t1.sec);

printf("\n Enter the second time in hrs, mins, and secs: ");

scanf("%d %d %d", &t2.hr, &t2.min, &t2.sec);

break;

case 2:

printf("\n The first time is: %d hr %d min %d sec", t1.hr, t1.min, t1.sec);

printf("\n The second time is: %d hr %d min %d sec", t2.hr, t2.min, t2.sec);

break;

case 3:

t3 = add time (t1, t2);

printf("\n The sum of the two time values is: %d hr %d min %d sec", t3.hr, t3.min, t3.sec);

break;

case 4:

t4 = subtract_time (t1, t2);

printf("\n The difference in time is: %d hr %d min %d sec", t4.hr, t4.min, t4.sec);

break;

}

} while (option != 5);

getch();

return 0;

}

TIME add_time (TIME t1, TIME t2)

{

TIME sum;

sum.sec = t1.sec + t2.sec;

while (sum.sec >= 60)

{

sum.min =60;

sum.hr++;

}

sum.min = t1.min + t2.min;

while(sum.min >= 60)

{

sum.sec -=60;

sum.min++;

}

sum.hr = t1.hr + t2.hr;

return sum;

}

TIME subtract_time (TIME t1, TIME t2)

{

TIME sub;

if (tl.hr > t2.hr)

{

if (tl.sec < t2.sec)

{

t1.sec += 60;

t1.min--;

}

sub.sec = tl.sec - t2.sec;

if (t1.min < t2.min)

{

t1.min += 60;

t1.hr--;

}

sub.min = t1.min - t2.min;

sub.hr = t1.hr - t2.hr;

}

else

{

if (t2.sec < tl.sec)

{

t2.sec += 60;

t2.min--;

}

sub.sec = t2.sec  -t1.sec;

if (t2.min < t1.min)

{

t2.min += 60;

t2.hr--;

}

sub.min = t2.min - t1.min;

sub.hr = t2.hr - t1.hr;

}

return sub;

}

Output

**** MAIN MENU ****

1. Read time

2. Display time

3. Add

4. Subtract

5. EXIT

Enter your option: 1

Enter the first time in hrs, mins, and secs:

2 30 20

Enter the second time in hrs, mins, and secs:

3 20 30

**** MAIN MENU ****

1. Read time

2. Display time

3. Add

4. Subtract

5. EXIT

Enter your option: 3

The sum of the two time values is: 5 hr 50

min 50 sec

Let us summarize some points that must be considered while passing a structure to a function.

• If the called function is returning a copy of the entire structure then its return type must be declared as struct followed by the structure name.

• The structure variable used as parameter in the function declaration must be the same as that of the actual argument in the called function (and that should be the name of the struct type).

• When a function returns a structure then in the calling function the returned structure must be assigned to a structure variable of the same type.

Passing Structures Through Pointers

Programming Tip: Using pointers to pass a structure to a function is more efficient than using the call-by-value method.

Passing large structures to functions using the call-by- value method is very inefficient. Therefore, it is preferred to pass structures through pointers. It is possible to create a pointer to almost any type in C, including user-defined types. It is extremely common to create pointers to structures. As in other cases, a pointer to a structure is never itself a structure, but merely a variable that holds the address of a structure. The syntax to declare a pointer to a structure can be given as

struct struct name

{

data_type member_name1;

data_type member_name2;

data_type member_name3;

……………………………..

}*ptr;

OR

struct struct_name *ptr;

For our student structure can declare a pointer we variable by writing

struct student *ptr_stud, stud;

The next thing to do is to assign the address of stud to the pointer using the address operator (&) as we would do in case of any other pointer. So to assign the address, we will write

Ptr_stud = &stud;

To access the members of the structure, one way is to write

/* get the structure, then select a member */ (*ptr_stud). roll_no;

Programming Tip: The selection operator (->) is a single token, so do not place any white space between them.

Since parentheses have a higher precedence than *, writing this statement would work well. But this statement is not easy for a beginner to work with. So C introduces a new operator to do the same task. This operator is known as the pointing-to operator (->). Here it is being used:

/* the roll_no in the structure ptr_stud points to */

ptr_stud -> roll_no = 01;

This statement is far easier than its alternative.

10. Write a program, using a pointer to a structure to initialize the members of the structure.

#include <stdio.h>

#include <conio.h>

struct student

{

int r no;

char name [20];

char course [20];

int fees;

};

int main()

{

struct student studl, stud2, *ptr_stud1,

*ptr_stud2;

clrscr();

ptr_studl = &stud1;

ptr_stud2 = &stud2;

ptr_stud1-> r_no = 01;

strcpy (ptr_stud1 -> name, "Rahul ");

strcpy (ptr_stud1-> course, "BCA");

ptr_stud1 -> fees = 45000;

printf("\n Enter the details of the second student: ");

printf("\n Enter the Roll Number = ");

scanf("%d", &ptr_stud2 -> r_no);

printf("\n Enter the Name =");

gets(ptr_stud2 ->name);

printf("\n Enter the Course =");

gets (ptr_stud2 -> course);

printf("\n Enter the Fees = " );

scanf("%d", &ptr_stud2 -> fees);

printf("\n DETAILS OF FIRST STUDENT");

printf("\n ROLL NUMBER = %d", ptr_studl->r_no);

printf("\n NAME = %s", ptr_stud1 ->name);

printf("\n COURSE = %s", ptr_stud1->course);

printf("\n FEES = %d", ptr_stud1 -> fees);

printf("\n\n\n\n DETAILS OF SECOND STUDENT");

printf("\n ROLL NUMBER = %d", ptr_stud2->r_no);

printf("\n NAME = %s", ptr_stud2 ->name);

printf("\n COURSE = %s", ptr_stud2->course);

printf("\n FEES = %d", ptr_stud2 -> fees);

return 0;

}

 

Output

Enter the details of the second student:

Enter the Roll Number = 02

Enter the Name = Aditya

Enter the Course = MCA

Enter the Fees = 60000

DETAILS OF FIRST STUDENT

ROLL NUMBER = 01

NAME = Rahul

NAME = Aditya

COURSE = MCA

FEES = 60000.00

 

-> roll_n_no = 0;

20

11. Write a program, using a pointer to a structure, to initialize the members of the structure using an alternative technique.

#include <stdio.h>

#include <conio.h>

struct student

{

int r_no;

char name [20];

char course [20];

float fees;

};

int main()

{

struct student *ptr_stud1;

struct student stud1 = {01, "Rahul", "BCA", 45000};

clrscr();

ptr_stud1 = &stud1;

printf("\n DETAILS OF STUDENT");

printf("\n ROLL NUMBER = %d", ptr_studl->r_no);

printf("\n NAME = %s", ptr_stud1 -> name);

printf("\n COURSE = %s", ptr_studl-> course);

printf("\n FEES = %f", ptr_stud1 -> fees);

return 0;

}

Output

DETAILS OF STUDENT

ROLL NUMBER = 01

NAME = Rahul

COURSE = BCA

FEES = 45000.00

12. Write a program, using an array of pointers to a structure, to read and display the data of a student.

#include <stdio.h>

#include <conio.h>

#include <alloc.h>

typedef struct student

{

int r_no;

char name [20];

char course [20];

int fees;

};

struct student *ptr [10];

int main()

{

int i;

for (i=0;i<2; i++)

{

ptr[i] = (struct student *)malloc(size of (struct student));

printf("\n Enter the data for student %d ",i+1);

printf("\n ROLL NO.: ");

scanf("%d", &ptr[i]->r_no);

printf("\n NAME: ");

gets (ptr[i] ->name);

printf("\n COURSE: ");

gets (ptr[i] -> course);

printf("\n FEES: ");

scanf("%d", &ptr[i] -> fees);

}

printf("\n DETAILS OF STUDENTS");

for (i=0;i<2; i++)

{

printf("\n ROLL NUMBER = %d", ptr_stud[i] => r_no);

printf("\n NAME = %s", ptr_stud[i] ->name);

printf("\n COURSE = %s", ptr_stud[i] -> course);

printf("\n FEES = %d",ptr_stud[i] -> fees);

}

return 0;

}

Output

Enter the data for student 1

ROLL NO.: 01

NAME: Rahul

COURSE: BCA

FEES: 45000

Enter the data for student 2

ROLL NO.:02

NAME: Priya

COURSE: BCA

FEES: 25000

DETAILS OF STUDENTS

ROLL NUMBER = 1

NAME = Rahul

COURSE = BCA

FEES = 45000

ROLL NUMBER = 2

NAME = Priya

COURSE = BCA

FEES = 25000

13. Write a program to read, display, add, and subtract two heights. Height should be given in feet and inches.

#include <stdio.h>

#include <conio.h>

typedef struct

{

int ft;

int inch;

}HEIGHT;

HEIGHT h1, h2, h3;

HEIGHT add_height (HEIGHT *,HEIGHT *);

HEIGHT subtract_height (HEIGHT*, HEIGHT *);

int main()

{

int option;

clrscr();

do

{

printf("\n *** MAIN MENU ***" );

printf("\n 1. Read height ");

printf("\n 2. Display height ");

printf("\n 3. Add");

printf("\n 4. Subtract");

printf("\n 5. EXIT");

printf("\n Enter your option: ");

scanf("%d", &option);

switch (option)

{

case 1:

printf("\n Enter the first height in feet and inches: ");

scanf("%d %d", &hl.ft, &hl.inch);

printf("\n Enter the second height in feet and inches: ");

scanf("%d %d", &h2. ft, &h2.inch);

break;

case 2:

printf("\n The first height is: %d ft %d inch", hl. ft, hl.inch);

printf("\n The second height is: %d ft %d inch", h2. ft, h2.inch);

break;

case 3:

h3 = add_height (&h1, &h2);

printf("\n The sum of two heights is: %d ft %d inch", h3. ft, h3.inch);

break;

case 4:

h3 = subtract_height (&hl, &h2);

printf("\n The difference of two heights is: %d ft %d inch", h3.ft, h3.inch);

break; }

}        `

} while (option != 5);

getch();

return 0;

}

HEIGHT add_height (HEIGHT *h1, HEIGHT *h2)

{

HEIGHT sum;

sum.inch = h1-> inch + h2 -> inch;

while (sum. inch > 12)

{

sum.inch - = 12;

sum.ft++;

}

sum.ft = h1-> ft + h2->ft;

return sum;

}

HEIGHT subtract_height (HEIGHT *h1, HEIGHT *h2)

{

HEIGHT sub;

if (hl->ft > h2-> ft)

{

if (h1-> inch <h2 -> inch)

{

h1-> inch += 12;

h1 -> ft--;

}

sub.inch = h1-> inch -  h2->inch;

sub.ft = h1-> ft - h2 -> ft;

}

else

{

if (h2 -> inch < h1 -> inch)

{

h2 -> inch += 12;

h2->ft--;

}

sub.inch = h2 -> inch - h1 -> inch;

sub.ft = h2 -> ft - h1-> ft;

}

return sub;

}

Output

*** MAIN MENU ***

1. Read height

2. Display height

3. Add

4. Subtract

5. EXIT

Enter your option: 1

Enter the first height in feet and inches: 2 3

Enter the second height in feet and inches: 4 5

*** MAIN MENU ***

1. Read height

2. Display height

3. Add

4. Subtract

5. EXIT

Enter your option: 3

The sum of two heights is: 6 ft 8 inch

14. Write a program that passes a pointer to a structure to a function.

#include <stdio.h>

#include <conio.h>

#include <alloc.h>

typedef struct student

{

int r_no;

char name [20];

char course [20];

int fees;

};

void display (struct student *);

int main()

{

struct student *ptr;

ptr = (struct student *)malloc(sizeof (struct student));

printf("\n Enter the data for the student ");

printf("\n ROLL NO.: ");

scanf("%d", &ptr->r_no);

printf("\n NAME: ");

gets (ptr->name);

printf("\n COURSE: ");

gets (ptr-> course);

printf("\n FEES: ");

scanf("%d", &ptr -> fees);

display (ptr);

getch();

return 0;

}

void display (struct student *ptr)

{

printf("\n DETAILS OF STUDENT");

printf("\n ROLL NUMBER = %d", ptr->r_no);

printf("\n NAME = %s", ptr->name);

printf("\n COURSE = %s", ptr->course)

printf("\n FEES = %d", ptr-> fees);

}

Output

Enter the data for the student

ROLL NO.: 01

NAME: Rahul

COURSE: BCA

FEES: 45000

DETAILS OF STUDENT

ROLL NUMBER = 01

NAME = Rahul

COURSE = BCA

FEES = 45000.00

15. Write a program to illustrate the use of arrays within a structure.

#include <stdio.h>

#include <conio.h>

#include <alloc.h>

typedef struct student

{

char name [20];

int roll_no;

int marks [3];

};

void display (struct student* s)

{

int i;

printf("\n NAME = %s \n ROLL NO = %d\n", s->name, s->roll_no);

printf("\n MARKS = ");

for (i = 0; i < 3;i++)

printf("%d", s->marks [i]);

}

int main()

{

struct student *s [2];

int i,j;

clrscr();

for (i=0; i < 2;i++)

{

s[i]=(struct student*)

malloc(sizeof (struct student));

printf("\n\n Enter the name of student %d: ", i+1);

gets (s[i]->name);

printf("\n Enter the roll number of student %d: ", i+1);

scanf("%d", &s [i] -> roll_no);

printf("\n Enter the marks obtained in three subjects by student %d: ", i+1);

for(j = 0; j < 3;j++)

scanf("%d", &s [i] -> marks [j]);

}

printf("\n \n\n *****DETAILS***** " );

for (i=0;i<2; i++)

display (s[i]);

getch();

return 0;

}

Output

Enter the name of student 1: Goransh

Enter the roll number of student 1: 01

Enter the marks obt obtained in three e subjects by student 1: 99 100 99

Enter the name of student 2: Pranjal

Enter the roll number of student 2: 02

Enter the marks obtained in three subjects by student 2: 90 100 89

*****DETAILS*****

NAME = Goransh

ROLL NO = 01

MARKS = 99 100 99

NAME = Pranjal

ROLL NO = 02

MARKS = 90 100 89