Solidity Arrays

Preface

In Solidity, there are two kinds of arrays:

1. Fixed-size array:
   
   You must specify array length at declaration time.
   
   Example: uint[5] numbers;
   
   Once created, the length is not possible to change.

2. Dynamic-size array:
   
   No need to specify length at declaration.
   
   Example: uint[] numbers;
   
   The length can be changed at runtime (grow or shrink).

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Most common syntax

uint[5] numbers;                     // fixed size array
uint[] numbers;                      // dynamic array
numbers[i];                          // access by index
uint[] storage refToNumbers = numbers; // storage reference
function f(uint[] memory a) external { ... } // pass memory array
numbers.push(x);                     // append to end
numbers.pop();                       // remove the last element
uint n = numbers.length;             // get length
delete numbers[i];                   // reset value to default
for (uint i = 0; i < numbers.length; i++) { ... } // loop

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Memory Arrays

When declaring an array inside a function, you must use the memory keyword.

A memory array always have fixed size, so you cannot call push or pop.

You can use the new keyword to create a memory array based on a variable size.

Example:

function createMemoryArray(uint size) public pure returns (uint[] memory) {
    uint[] memory newArr = new uint[](size);
    return newArr;
}