Lesson 9 of 34
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# Structs

##### Yasin Cakal

In Solidity, structs are used to create custom data types that can store multiple variables of different types. Structs are a key concept in programming that allow you to create complex and reusable data structures, making it easier to manage and organize data in your contracts and decentralized applications. In this article, we’ll take a closer look at structs in Solidity, including how to define and use them, and how to access and modify their variables.

## Defining Structs

In Solidity, structs are defined using the “struct” keyword followed by the struct name and a set of curly braces containing the variables that the struct will contain. The variables in a struct can be of any data type, and multiple structs can be defined in a single contract.

For example, the following code defines a struct called “Person” that contains three variables: “name”, “age”, and “height”:

struct Person {
string name;
uint age;
uint height;
}


This struct can be used to store information about a person, such as their name, age, and height.

## Creating Struct Instances

To create an instance of a struct in Solidity, use the “new” keyword followed by the struct name and a set of parentheses. For example:

Person p = new Person();

This code creates a new instance of the “Person” struct called “p”.

## Accessing and Modifying Struct Variables

To access or modify a variable in a struct instance, use the instance name followed by a period and the variable name. For example:

p.name = "Alice";
p.age = 25;
p.height = 170;


This code sets the “name” variable of the “p” struct instance to “Alice”, the “age” variable to 25, and the “height” variable to 170.

To access the value of a struct variable, use the instance name followed by a period and the variable name. For example:

string name = p.name;
uint age = p.age;
uint height = p.height;


This code retrieves the values of the “name”, “age”, and “height” variables in the “p” struct instance and stores them in separate variables.

## Passing Structs as Function Parameters

In Solidity, structs can be passed as function parameters in the same way as other data types. For example:

function setPerson(Person person) public {
person.name = "Bob";
person.age = 30;
person.height = 180;
}


This function defines a parameter called “person” of type “Person” and modifies its “name”, “age”, and “height” variables.

## Conclusion

In conclusion, structs in Solidity are a useful tool for creating custom data types that can store multiple variables of different types. Structs are defined using the “struct” keyword and instances are created using the “new” keyword. Struct variables can be accessed and modified using the instance name followed by a period and the variable name. Structs can be passed as function parameters and are a useful way to manage and organize data in Solidity contracts and decentralized applications.

## Exercises

To review these concepts, we will go through a series of exercises designed to test your understanding and apply what you have learned.

#### What is a struct in Solidity?

In Solidity, a struct is a custom data type that is used to store multiple variables of different types. Structs are a key concept in programming that allow you to create complex and reusable data structures, making it easier to manage and organize data in your contracts and decentralized applications.

#### How are structs defined in Solidity?

In Solidity, structs are defined using the “struct” keyword followed by the struct name and a set of curly braces containing the variables that the struct will contain. The variables in a struct can be of any data type, and multiple structs can be defined in a single contract.

#### How do you create an instance of a struct in Solidity?

To create an instance of a struct in Solidity, use the “new” keyword followed by the struct name and a set of parentheses. For example: “Person p = new Person();”.

#### How do you access and modify the variables in a struct instance in Solidity?

To access or modify a variable in a struct instance in Solidity, use the instance name followed by a period and the variable name. For example: “p.name = “Alice”;”.

#### Can structs be passed as function parameters in Solidity?

Yes, in Solidity, structs can be passed as function parameters in the same way as other data types. For example: “function setPerson(Person person) public { … }”.