C Programming Lesson - Structures in C

We used variable in our C program to store value but one variable can store only single piece information (an integer can hold only one integer value) and to store similar type of values we had to declare many variables. To overcome this problem we used array which can hold numbers of similar data type. But array too have some limitations, like in our real world application we deal with set of dissimilar data types and single array cannot store dissimilar data.

For example think about storing book information or product information, a product can have different information to store like product code (an integer), product name (a char array), product price (a float) etc. And to store 20 products information we can declare integer array for product code, 2D character array for storing product name and float array to store product price. This approach definitely achieves your goals, but try to consider these things too. What if you wanted to add more products than 20, what if you want to add more information on products like stock, discount, tax etc? It will become difficult to differentiate these variables with other variables declared for calculation etc.

To solve this problem C language has a unique data type called Structure. C structure is nothing but collection of different related data types. If we are using C structure then we are combining different related data types in one group so that we can use and manage those variables easily. Here related data type means, a structure holding information about book will contains variable and array related to book. 

struct structure_name
{
data type member1;
data type member2;
…
…
};

Example:

struct products
{
char name[20];
int stock;
float price;
};

So structure declaration begins with struct keyword and with a space we need to provide a structure name. Within open and closed curly braces we can declare required and related variable, you can see it in our example structure declaration. And most important point to remember in case of C structure is that it ends with semicolon (;).

Let’s have a complete example of structure in C language.

So line no.4-9 declares a C structure named “product”, this structure contains four variables to store different information about product. In the beginning there is a character array (char name[30]) which stores name of the product, next we have integer variable (int stock) to store stock of product and last two variable are float type (float price, discount) to product price & discount on product respectively.

Guys we just declared product structure and now we have to use it in main(). Line no. 14 declares a product type variable p1. Here product type variable means, in our C program product is a structure and to use that structure we need to create its variable. Declaring a product structure variable is simple just use following syntax:

struct structure_name variable_name;

Remember struct is a C keyword, “structure_name” is name of structure you used while declaring a C structure (in above C program its product) and “variable_name” could be any name of your choice (in above C program its p1) but standard naming convention applies.

Along with declaring C structure variable p1 we have also initialized it and to initialize C structure you need to assign values in proper order. Proper order means assign value in the order they are declared in structure. For example, in our product structure we declare variable in following orders:

char name[30];
int stock;
float price, discount;

So for this structure proper order will be:

char name[30];
int stock;
float price;
float discount;

You don’t need to rewrite your structure, you just need to keep it in mind that structure variable initialization should be performed in orderly manner (top – bottom and left – right manner) otherwise it will show error or you may get strange output.

So in above program we have initialized p1 variable in following way:

struct product p1 ={"Apple iPod Touch 32GB", 35, 298.56, 2.32}; means

struct product p1 ={char name[30], int stock, float price, float discount}; //this line of code is only assumption.

Next in line no. 16 we just printed the values stores in product structure. You cannot print values stored in product structure member variable (like name, stock etc.) directly, you have to link member variable with structure variable and you can do this using (.) dot operator. For example: character array name is unknown to main() because it is declared in structure product, so to access member variable we will follow the following syntax:

structure_variable.member_variable;

Example:

p1.name;

We can rewrite printf("Name=%s,\nStock=%d,\nPrice=$%.2f,\nDiscount=%.2f%.", p1.name, p1.stock, p1.price,p1.discount); in the following manner:

printf(“Name = %s”,p1.name);
printf(“Stock = %d”,p1.stock);
printf(“Price = $%.2f”,p1.price);
printf(“Stock = %.2f”,p1.discount);

Here is full working code sample of C Structure.

I hope this will help you understand C Structure, we will see more C structure example code in my next tutorial. If you have any question regarding this topic please drop comment. Thanks for dropping in.