C Structures: Declaration, Access, Initialization, and Arrays, Slides of Computer Science

Download C Structures: Declaration, Access, Initialization, and Arrays and more Slides Computer Science in PDF only on Docsity!

STRUCTURES

1

Contents

• Overview
• Structure and their variables declaring
• Accessing the members of a Structure
• Initialization of Structures
• Copying and Comparing Structures
• Nesting of Structures
• Arrays of Structures
• Structures and Pointers
• Structures and Functions (^2)

Structure and their variables declaring

• Structure is declared by using the keyword called struct
• The struct is followed by the body of the structure
• Within the body of structure we declares variables or members of the structure
• The format is as follows: struct { <data type member_name 1 >; <data type member_name 2 >; ….. ; } <structure_variable 1 >,<structure_variable 2 >,…;
• In the above format structuretagname is optional and not needed if the structure variables are defined
• The body of structure contain any number of variables separated by semicolons
• Whereas at the end structure_variables define the actual names of the individual structures 4

Structure and their variables declaring

• structure_variables can be defined separately by specifying the following declaration statement:
• struct <structure_variable>;
• This creates the structure_variables and has a separate instance of all the member_names in structure tag name.
• For example 1 :
• Declaration of structures and definition of structure variables. OR
• The above statement is defining the variables of character type called name , integer type called roll_no , and character type called address 5

struct students

char name[ 30 ];

int roll_no[ 6 ];

char address[ 30 ];

}abc, xyz;

struct students

char name[ 30 ];

int roll_no[ 6 ];

char address[ 30 ];

struct students abc, xyz;

Accessing the members of a Structure

• The members of a structure can be accessed using the ‘.’, which is called ‘dot operator’.
• The members are accessed by relating them to the structure variable with a dot operator
• The general form of the statement for accessing a member of a structure is as follows:
• <structure_variable>.<member_name>;
• For example 3 : struct abc { int a; int b; int c; }ab, bc; The first member can be accessed by the construct ab.a; 7

Accessing the members of a Structure

• We can also assign a value to the member of the structure
• Suppose we want to access the value 100 , say to member c identified by the variable bc , thus the statement can be written as:
• bc.c = 100 ;
• To print this value assigned to the member on the screen, the following code is written:
• printf(“%d”, bc.c);
• To input the value of c , the following code can be used:
• scanf(“%d”, bc.c);
• Now consider the another structure which are as follows: struct personal_data { int rollno[ 6 ]; char name[ 30 ]; char address[ 30 ]; }; (^8)

Initialization of Structures

• A structure can be initialized in much the same way as any other data type
• This consists of assigning some constants to the member of the structure
• Structures that are not explicitly initialized by the programmer are, by default, initialized by the system
• The general construct for initializing a structure can be any of the two forms given as follows: struct <structure_tag_name> { <data_type member_name 1 >; <data_type member_name 2 >; …. }<structure_variable> = {constant 1 , constant 2 ,.. .}; OR struct<structure_tag_name><structure_variable> = {constant 1 , …}; 10

Initialization of Structures

• The following are some examples using both the forms of initialization:
• For example 4 :
• Initialization of structure using the first construct #include <stdio.h> struct medicine { int count; int m_date, m_month, m_year; int ex_date, ex_month, ex_year; }batch={ 1000 , 10 , 04 , 2018 , 20 , 09 , 2019 }; main() { printf(“\n count=%d”, batch.count); printf(“\n mfg-date=%d%d%d”, batch.m_date, batch.m_month, batch.m_year); printf(“\n exp-date=%d%d%d”, batch.ex_date, batch.ex_month, batch.ex_year);} 11

Copying and Comparing Structures

• A structure can be assigned to another structure of the same type
• For example 6 :
• Copying one structure to another of the same type #include<stdio.h> struct employee{ char grade; int basic; float allowance; }; main() { struct employee abc={‘a’, 7000 , 650. 50 }; struct employee xyz; xyz=abc; printf(“\n The grade of xyz ix %c, basic is Rs %d, allowance is Rs %f”, xyz.grade, xyz.basic, xyz.allowance); return 0 ;} 13

Copying and Comparing Structures

• Comparing one structure variable with another is not allowed in C.
• However, members of one structure can be compared with members of another on an individual basis
• In fact, the members involved in the comparison will behave like any other variable
• For example 7 :
• Comparison of individual members of structures #include<stdio.h> struct employee{ char grade; int basic; float allowance; }; main() { struct employee abc={‘a’, 7000 , 650. 50 }; (^14)

Nesting of Structures

• A structure can be placed within another structure
• In other words, structures can contain other structures as members
• A structure within a structure means nesting of structures
• In such cases, the dot operator in conjunction with the structure variables are used to access the members of the innermost as well as outermost structures.
• For example 8 :
• A C program to demonstrate nesting of structures and accessing structure members #include<stdio.h> struct outer {int out 1 ; float out 2 ; struct inner {int in 1 ; float in 2 ;}invar; }; (^16)

Nesting of Structures

main() { struct outer outvar; outvar.out 1 = 2 ; outvar.out 2 = 20. 50 ; outvar.invar.in 1 = 3 ; outvar.invar.in 2 = 30. 50 ; printf(“out 1 =%d, out 2 =% 6. 2 f, in 1 =%d, in 2 =% 6. 2 f”, outvar.out 1 , outvar.out 2 , outvar.invar.in 1 , outvar.invar.in 2 ); return 0 ; } 17

Arrays of Structures

struct demo {char a; int i; float f; }d[ 3 ]; main() { int n; for(n= 0 ;n<= 2 ; ++n) { printf(“\nEnter ch, in, f 1 :”); scanf(“%c %d %f”, &(d[n].a), &(d[n].i), &(d[n].f); printf(“\n a=%c, i=%d, u=%f”, d[n].a, d[n].i, d[n].f); } return 0 ; } 19

Structures and Pointers

• A pointer to a structure is not itself a structure, but merely a variable that holds the address of the structure
• Declaring pointers to a structure is basically the same as declaring a normal pointer
• Syntax: struct <structure_tag_name> { <datatype n 1 >; <datatype n 2 >; …. ; }*ptr; OR struct <structure_tag_name> *ptr;
• This pointer *ptr can be assigned to any other pointer of the same type
• It can be used to access the members of its structure (^20)