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Structures in C ”; Previous Next Structures in C A structure in C is a derived or user-defined data type. We use the keyword struct to define a custom data type that groups together the elements of different types. The difference between an array and a structure is that an array is a homogenous collection of similar types, whereas a structure can have elements of different types stored adjacently and identified by a name. We are often required to work with values of different data types having certain relationships among them. For example, a book is described by its title (string), author (string), price (double), number of pages (integer), etc. Instead of using four different variables, these values can be stored in a single struct variable. Declare (Create) a Structure You can create (declare) a structure by using the “struct” keyword followed by the structure_tag (structure name) and declare all of the members of the structure inside the curly braces along with their data types. To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member. Syntax of Structure Declaration The format (syntax) to declare a structure is as follows − struct [structure tag]{ member definition; member definition; … member definition; } [one or more structure variables]; The structure tag is optional and each member definition is a normal variable definition, such as “int i;” or “float f;” or any other valid variable definition. At the end of the structure”s definition, before the final semicolon, you can specify one or more structure variables but it is optional. Example In the following example we are declaring a structure for Book to store the details of a Book − struct book{ char title[50]; char author[50]; double price; int pages; } book1; Here, we declared the structure variable book1 at the end of the structure definition. However, you can do it separately in a different statement. Structure Variable Declaration To access and manipulate the members of the structure, you need to declare its variable first. To declare a structure variable, write the structure name along with the “struct” keyword followed by the name of the structure variable. This structure variable will be used to access and manipulate the structure members. Example The following statement demonstrates how to declare (create) a structure variable struct book book1; Usually, a structure is declared before the first function is defined in the program, after the include statements. That way, the derived type can be used for declaring its variable inside any function. Structure Initialization The initialization of a struct variable is done by placing the value of each element inside curly brackets. Example The following statement demonstrates the initialization of structure struct book book1 = {“Learn C”, “Dennis Ritchie”, 675.50, 325}; Accessing the Structure Members To access the members of a structure, first, you need to declare a structure variable and then use the dot (.) operator along with the structure variable. Example 1 The four elements of the struct variable book1 are accessed with the dot (.) operator. Hence, “book1.title” refers to the title element, “book1.author” is the author name, “book1.price” is the price, “book1.pages” is the fourth element (number of pages). Take a look at the following example − #include <stdio.h> struct book{ char title[10]; char author[20]; double price; int pages; }; int main(){ struct book book1 = {“Learn C”, “Dennis Ritchie”, 675.50, 325}; printf(“Title: %s n”, book1.title); printf(“Author: %s n”, book1.author); printf(“Price: %lfn”, book1.price); printf(“Pages: %d n”, book1.pages); printf(“Size of book struct: %d”, sizeof(struct book)); return 0; } Output Run the code and check its output − Title: Learn C Author: Dennis Ritchie Price: 675.500000 Pages: 325 Size of book struct: 48 Example 2 In the above program, we will make a small modification. Here, we will put the type definition and the variable declaration together, like this − struct book{ char title[10]; char author[20]; double price; int pages; } book1; Note that if you a declare a struct variable in this way, then you cannot initialize it with curly brackets. Instead, the elements need to be assigned individually. #include <stdio.h> #include <string.h> struct book{ char title[10]; char author[20]; double price; int pages; } book1; int main(){ strcpy(book1.title, “Learn C”); strcpy(book1.author, “Dennis Ritchie”); book1.price = 675.50; book1.pages = 325; printf(“Title: %s n”, book1.title); printf(“Author: %s n”, book1.author); printf(“Price: %lf n”, book1.price); printf(“Pages: %d n”, book1.pages); return 0; } Output When you execute this code, it will produce the following output − Title: Learn C Author: Dennis Ritchie Price: 675.500000 Pages: 325 Copying Structures The assignment (=) operator can be used to copy a structure directly. You can also use the assignment operator (=) to assign the value of the member of one structure to another. Let”s have two struct book variables, book1 and book2. The variable book1 is initialized with declaration, and we wish to assign the same values of its elements to that of book2. We can assign individual elements as follows − struct book book1 = {“Learn C”, “Dennis Ritchie”, 675.50, 325}, book2; strcpy(book2.title, book1.title); strcpy(book2.author, book1.author); book2.price = book1.price; book2.pages = book1.pages; Note the use of strcpy() function to assign the value to a string variable instead of using the “= operator”. Example You can also assign book1 to book2 so that all the elements of book1 are respectively assigned to the elements of book2. Take a look at the following program code − #include <stdio.h> #include <string.h> struct book{ char title[10];