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# Variables

##### Yasin Cakal

As a Solidity developer, it’s important to have a strong understanding of variables – one of the most fundamental concepts in programming. In this article, we’ll take a closer look at variables in Solidity, including how to declare them, the different types of variables available, and how to use them in your code.

## What are Variables?

In programming, a variable is a named location in memory where a value can be stored and accessed. Variables are used to store data that can be used and manipulated by the program.

In Solidity, variables are declared using the “var” keyword, followed by the variable name and the type of data that the variable will hold. For example:

var myVariable uint256;

This code declares a variable called “myVariable” that can hold an unsigned integer (uint) of 256 bits.

## Types of Variables in Solidity

Solidity supports a wide range of variable types, including integers, booleans, and strings. Here are some of the most commonly used variable types in Solidity:

• uint: Unsigned integer (positive whole number)
• int: Signed integer (positive or negative whole number)
• bool: Boolean (true or false)
• string: String (sequence of characters)

In addition to these basic types, Solidity also supports arrays, mappings, and structs, which allow you to store more complex data structures.

Arrays are used to store a list of items of the same type. For example:

uint[] myArray;

This code declares an array of unsigned integers called “myArray”.

Mappings are used to store key-value pairs, similar to a dictionary in other languages. For example:

mapping(address => uint) balances;

This code declares a mapping called “balances” that maps addresses (the keys) to unsigned integers (the values).

Structs are used to define custom data types that can be composed of several different types. For example:

struct User {
string name;
uint age;
}


This code declares a struct called “User” that has two fields: a string called “name” and an unsigned integer called “age”.

## Using Variables in Solidity

Once you’ve declared a variable, you can use it in your code by referencing its name. For example:

function setAge(uint newAge) public {
age = newAge;
}


This code defines a function called “setAge” that takes an unsigned integer as an argument and assigns it to the “age” variable.

You can also access the value of a variable by referencing its name. For example:

function getAge() public view returns (uint) {
return age;
}


This code defines a function called “getAge” that returns the value of the “age” variable.

## Conclusion

In conclusion, variables are a fundamental concept in programming that are used to store and manipulate data in a program. In Solidity, variables are declared using the “var” keyword and can be of several different types, including integers, booleans, and strings. Once a variable has been declared, it can be used and accessed in your code by referencing its name. Understanding how to use variables is essential for building effective 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 variable in programming?

In programming, a variable is a named location in memory where a value can be stored and accessed.

#### How are variables declared in Solidity?

In Solidity, variables are declared using the “var” keyword, followed by the variable name and the type of data that the variable will hold. For example: “var myVariable uint256;”.

#### What is an array in Solidity?

An array in Solidity is used to store a list of items of the same type. For example: “uint[] myArray;”.

#### What is a mapping in Solidity?

A mapping in Solidity is used to store key-value pairs, similar to a dictionary in other languages. For example: “mapping(address => uint) balances;”.

#### What is a struct in Solidity?

A struct in Solidity is used to define a custom data type that can be composed of several different types. For example: “struct User { string name; uint age; }”.