Data Structure and Control Structure in Solidity

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Hello Reader, Do you know what are data structures? If not then here is what data structures mean.

data structure is a particular way of organising data in a computer memory so that it can be used effectively.

Solidity provides three types of data structures:

  1. Structs
  2. Arrays
  3. Mappings
Solidity Data Structures
Solidity Data Structures

One by one let us look at each data structure.


Solidity provides a way to define new types in the form of structs. A struct is a special data type that allows the programmer to group a list of variables.

pragma solidity ^0.4.0;
contract Ballot {
struct Voter { // Struct
uint weight1, weight2, weight3;
bool voted;
address delegate1, delegate2, delegate3, delegate4;
string name;
uint vote1, vote2, vote3, vote4, vote5;
uint height1, height2, height3   } }

Structs allow you to create more complicated data types that have multiple properties.

Structs can only have 16 members, exceeding which the following error might occur: Stack too Deep.


Now, what if you need a collection of something, say addresses. Well, just like most of the languages, Solidity also has Arrays.

When you want a collection of something, you can use an array. There are two types of arrays in Solidity : fixed arrays and dynamic arrays.

Array with a fixed length of 2 elements, containing integers :
uint[2] fixedArray;

Another fixed Array, can contain 5 strings :
string[5] stringArray;

A dynamic Array — has no fixed size, can keep growing:
uint[] dynamicArray;

An array of structs :
StructName[] variablename;

Working With Structs and Arrays

Consider the Struct we previously created

struct MyProfile{
 string firstname;
 string lastname;
 uint16 age;
 bool isMarried;
MyProfile[] public people;

Now let’s see how to create new Person’s objects and add them to our people array.

Create a New Person:

Person James = Person(“James”,”Ryan”,35,true);

Add that person to the Array:


We can also combine these together and do them in one line of code to keep things clean:



Mappings allow the programmer to create key-value pairs for storing(as a list) and looking up data.

It can be seen as hash tables which are virtually initialized such that every possible key exists and is mapped to a value whose byte-representation is all zeros: a type’s default value.

Two commonly used data types [ key_type ] for mapping keys are address and uint.
It is important to note that not every data type can be used as a key. For instance, structs and other mappings cannot be used as keys.
Unlike with keys, Solidity does not limit the data type for values [ key_values ]. It can be anything, including structs and other mappings.

Mappings are declared as:

Mapping(_Keytype => _ValueType )

_Keytype can be almost any type except for a dynamically sized array, a contract, an enum and a struct.

contract MappingExample {
mapping(address => uint) public balances;
function update(uint newBalance) {
balances[msg.sender] = newBalance;  }}
contract MappingUser {
function f() returns (uint) {
MappingExample m = new MappingExample();
return m.balances(this);

Control Structures

Solidity follows the same syntax of control structures as Java script or C.
So there is: if, else, while, do, for, break, continue, with the usual semantics known from C or JavaScript.

There is no type conversion from non-boolean to boolean types as there is in C and JavaScript.

Now let’s see how these Control structures are used in Solidity.

contract ControlStructure {
address public variable1;
function ControlStructure>){

// if-else can be used like this

// while can be used like this

// for loop can be used like this
for(uint i=0;i<=50;i++) 
    variable1++; if(variable1==4) break; 

//do while can be used like this 
do { variable1--; } (while variable1>0);

// Conditional Operator can be used like this
bool IsTrue = (variable1 == 1)?true: false;
/*will show an error because
there is no type conversion from non-boolean to boolean

So here we wrap up control structures and Data Structures in Solidity.

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Written by 

Ayushi is a Software Developer having more than 1.5 year of experience in RUST. Her practice area is Rust and Go. She loves to solve daily coding challenges.