C Programming Structure
Structure is the collection of variables of different types under a single name for better handling. For example: You want to store the information about person about his/her name, citizenship number and salary. You can create these information separately but, better approach will be collection of these information under single name because all these information are related to person.
Structure Definition in C
Keyword
struct is used for creating a structure.Syntax of structure
struct structure_name
{
data_type member1;
data_type member2;
.
.
data_type memeber;
};
We can create the structure for a person as mentioned above as:
struct person
{
char name[50];
int cit_no;
float salary;
};
This declaration above creates the derived data type
struct person.Structure variable declaration
When a structure is defined, it creates a user-defined type but, no storage is allocated. For the above structure of person, variable can be declared as:
struct person
{
char name[50];
int cit_no;
float salary;
};
Inside main function:
struct person p1, p2, p[20];
Another way of creating sturcture variable is:
struct person
{
char name[50];
int cit_no;
float salary;
}p1 ,p2 ,p[20];
In both cases, 2 variables p1, p2 and array p having 20 elements of type struct person are created.
Accessing members of a structure
There are two types of operators used for accessing members of a structure.
- Member operator(.)
- Structure pointer operator(->) (will be discussed in structure and pointers chapter)
Any member of a structure can be accessed as:
structure_variable_name.member_name
Suppose, we want to access salary for variable p2. Then, it can be accessed as:
p2.salary
Example of structure
Write a C program to add two distances entered by user. Measurement of distance should be in inch and feet.(Note: 12 inches = 1 foot)
#include <stdio.h>
struct Distance{
int feet;
float inch;
}d1,d2,sum;
int main(){
printf("1st distance\n");
printf("Enter feet: ");
scanf("%d",&d1.feet); /* input of feet for structure variable d1 */
printf("Enter inch: ");
scanf("%f",&d1.inch); /* input of inch for structure variable d1 */
printf("2nd distance\n");
printf("Enter feet: ");
scanf("%d",&d2.feet); /* input of feet for structure variable d2 */
printf("Enter inch: ");
scanf("%f",&d2.inch); /* input of inch for structure variable d2 */
sum.feet=d1.feet+d2.feet;
sum.inch=d1.inch+d2.inch;
if (sum.inch>12){ //If inch is greater than 12, changing it to feet.
++sum.feet;
sum.inch=sum.inch-12;
}
printf("Sum of distances=%d\'-%.1f\"",sum.feet,sum.inch);
/* printing sum of distance d1 and d2 */
return 0;
}
Output
1st distance Enter feet: 12 Enter inch: 7.9 2nd distance Enter feet: 2 Enter inch: 9.8 Sum of distances= 15'-5.7"
Keyword typedef while using structure
Programmer generally
use typedef while using structure in C language. For example:typedef struct complex{
int imag;
float real;
}comp;
Inside main:
comp c1,c2;
Here,
typedef keyword is used in creating a type comp(which is of type as struct complex). Then, two structure variables c1 and c2 are created by this comp type.Structures within structures
Structures can be nested within other structures in C programming.
struct complex
{
int imag_value;
float real_value;
};
struct number{
struct complex c1;
int real;
}n1,n2;
Suppose you want to access imag_value for n2 structure variable then, structure membern1.c1.imag_value is used.
C Programming Structure and Pointer
Pointers can be accessed along with structures. A pointer variable of structure can be created as below:
struct name {
member1;
member2;
.
.
};
-------- Inside function -------
struct name *ptr;
Here, the pointer variable of type
struct name is created.
Structure's member through pointer can be used in two ways:
- Referencing pointer to another address to access memory
- Using dynamic memory allocation
Consider an example to access structure's member through pointer.
#include <stdio.h>
struct name{
int a;
float b;
};
int main(){
struct name *ptr,p;
ptr=&p; /* Referencing pointer to memory address of p */
printf("Enter integer: ");
scanf("%d",&(*ptr).a);
printf("Enter number: ");
scanf("%f",&(*ptr).b);
printf("Displaying: ");
printf("%d%f",(*ptr).a,(*ptr).b);
return 0;
}
In this example, the pointer variable of type
struct name is referenced to the address of p. Then, only the structure member through pointer can can accessed.
Structure pointer member can also be accessed using
-> operator.(*ptr).a is same as ptr->a (*ptr).b is same as ptr->b
Accessing structure member through pointer using dynamic memory allocation
To access structure member using pointers, memory can be allocated dynamically using malloc() function defined under
"stdlib.h" header file.Syntax to use malloc()
ptr=(cast-type*)malloc(byte-size)
Example to use structure's member through pointer using malloc() function.
#include <stdio.h>
#include<stdlib.h>
struct name {
int a;
float b;
char c[30];
};
int main(){
struct name *ptr;
int i,n;
printf("Enter n: ");
scanf("%d",&n);
ptr=(struct name*)malloc(n*sizeof(struct name));
/* Above statement allocates the memory for n structures with pointer ptr pointing to base address */
for(i=0;i<n;++i){
printf("Enter string, integer and floating number respectively:\n");
scanf("%s%d%f",&(ptr+i)->c,&(ptr+i)->a,&(ptr+i)->b);
}
printf("Displaying Infromation:\n");
for(i=0;i<n;++i)
printf("%s\t%d\t%.2f\n",(ptr+i)->c,(ptr+i)->a,(ptr+i)->b);
return 0;
}
Output
Enter n: 2
Enter string, integer and floating number respectively:
Programming
2
3.2
Enter string, integer and floating number respectively:
Structure
6
2.3
Displaying Information
Programming 2 3.20
Structure 6 2.30
C Programming Structure and Function
In C, structure can be passed to functions by two methods:
- Passing by value (passing actual value as argument)
- Passing by reference (passing address of an argument)
Passing structure by value
A structure variable can be passed to the function as an argument as normal variable. If structure is passed by value, change made in structure variable in function definition does not reflect in original structure variable in calling function.
Write a C program to create a structure student, containing name and roll. Ask user the name and roll of a student in main function. Pass this structure to a function and display the information in that function.
#include <stdio.h>
struct student{
char name[50];
int roll;
};
void Display(struct student stu);
/* function prototype should be below to the structure declaration otherwise compiler shows error */
int main(){
struct student s1;
printf("Enter student's name: ");
scanf("%s",&s1.name);
printf("Enter roll number:");
scanf("%d",&s1.roll);
Display(s1); // passing structure variable s1 as argument
return 0;
}
void Display(struct student stu){
printf("Output\nName: %s",stu.name);
printf("\nRoll: %d",stu.roll);
}
Output
Enter student's name: Kevin Amla Enter roll number: 149 Output Name: Kevin Amla Roll: 149
Passing structure by reference
The address location of structure variable is passed to function while passing it by reference. If structure is passed by reference, change made in structure variable in function definition reflects in original structure variable in the calling function.
Write a C program to add two distances(feet-inch system) entered by user. To solve this program, make a structure. Pass two structure variable (containing distance in feet and inch) to add function by reference and display the result in main function without returning it.
#include <stdio.h>
struct distance{
int feet;
float inch;
};
void Add(struct distance d1,struct distance d2, struct distance *d3);
int main()
{
struct distance dist1, dist2, dist3;
printf("First distance\n");
printf("Enter feet: ");
scanf("%d",&dist1.feet);
printf("Enter inch: ");
scanf("%f",&dist1.inch);
printf("Second distance\n");
printf("Enter feet: ");
scanf("%d",&dist2.feet);
printf("Enter inch: ");
scanf("%f",&dist2.inch);
Add(dist1, dist2, &dist3);
/*passing structure variables dist1 and dist2 by value whereas passing structure variable dist3 by reference */
printf("\nSum of distances = %d\'-%.1f\"",dist3.feet, dist3.inch);
return 0;
}
void Add(struct distance d1,struct distance d2, struct distance *d3)
{
/* Adding distances d1 and d2 and storing it in d3 */
d3->feet=d1.feet+d2.feet;
d3->inch=d1.inch+d2.inch;
if (d3->inch>=12) { /* if inch is greater or equal to 12, converting it to feet. */
d3->inch-=12;
++d3->feet;
}
}
Output
First distance Enter feet: 12 Enter inch: 6.8 Second distance Enter feet: 5 Enter inch: 7.5 Sum of distances = 18'-2.3"
Explaination
In this program, structure variables dist1 and dist2 are passed by value (because value of dist1and dist2 does not need to be displayed in main function) and dist3 is passed by reference ,i.e, address of dist3
(&dist3) is passed as an argument. Thus, the structure pointer variable d3 points to the address of dist3. If any change is made in d3 variable, effect of it is seed in dist3 variable in main function.C Programming Unions
Unions are quite similar to the structures in C. Union is also a derived type as structure. Union can be defined in same manner as structures just the keyword used in defining union in union where keyword used in defining structure was struct.
union car{
char name[50];
int price;
};
Union variables can be created in similar manner as structure variable.
union car{
char name[50];
int price;
}c1, c2, *c3;
OR;
union car{
char name[50];
int price;
};
-------Inside Function-----------
union car c1, c2, *c3;
In both cases, union variables c1, c2 and union pointer variable c3 of type
union car is created.Accessing members of an union
The member of unions can be accessed in similar manner as that structure. Suppose, we you want to access price for union variable c1 in above example, it can be accessed as
c1.price. If you want to access price for union pointer variable c3, it can be accessed as (*c3).price or as c3->price.Difference between union and structure
Though unions are similar to structure in so many ways, the difference between them is crucial to understand. This can be demonstrated by this example:
#include <stdio.h>
union job { //defining a union
char name[32];
float salary;
int worker_no;
}u;
struct job1 {
char name[32];
float salary;
int worker_no;
}s;
int main(){
printf("size of union = %d",sizeof(u));
printf("\nsize of structure = %d", sizeof(s));
return 0;
}
Output
size of union = 32 size of structure = 40
There is difference in memory allocation between union and structure as suggested in above example. The amount of memory required to store a structure variables is the sum of memory size of all members.
But, the memory required to store a union variable is the memory required for largest element of an union.
What difference does it make between structure and union?
As you know, all members of structure can be accessed at any time. But, only one member of union can be accessed at a time in case of union and other members will contain garbage value.
#include <stdio.h>
union job {
char name[32];
float salary;
int worker_no;
}u;
int main(){
printf("Enter name:\n");
scanf("%s",&u.name);
printf("Enter salary: \n");
scanf("%f",&u.salary);
printf("Displaying\nName :%s\n",u.name);
printf("Salary: %.1f",u.salary);
return 0;
}
Output
Enter name Hillary Enter salary 1234.23 Displaying Name: f%Bary Salary: 1234.2
Note: You may get different garbage value of name.
Why this output?
Initially, Hillary will be stored in
u.name and other members of union will contain garbage value. But when user enters value of salary, 1234.23 will be stored in u.salary and other members will contain garbage value. Thus in output, salary is printed accurately but, name displays some random string.Passing Union To a Function
Union can be passed in similar manner as structures in C programming. Visit this page to learn more about: How structure can be passed to function in C programming?
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