Control Structures and Data Structures in Solidity

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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.

Syntax of if-else block :

if(condition) 
    //do something         
else             
    //do something

Syntax of while loop :

while(condition){
    //do something
}

Syntax of for loop :

for(uint i = 0; i <= n; i++)
 {
    //do something     
 }

Syntax of do-while loop :

do{
  //do something
} while(condition);

Structs

A struct is a special data type that allows the programmer to group a list of variables.

Syntax :

struct MyProfile{
    string firstname;
    string lastname;
    uint16 age;
    bool isMarried;
}

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:
people.push(James);

We can also combine these together and do them in one line of code to keep things clean:
people.push(Person(“James”,”Ryan”,35,true));

Mappings

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

Syntax :
mapping(key_type => key_value) mappingName;

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.

A mapping to hold the bank account balance in uint for the given address :
mapping(address => uint) balance;

A mapping to store usernames based on userId :
mapping (uint => string) userIdToName;

Yay!!! 🎉 That wraps up the basics of control structures and data structures.

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