Functions

In this section, we will look at functions. Recall from the beginning of this course that all smart contracts consist of a state and their behaviors. With regards to the latter, functions allow us to define the behavior of a smart contract.

Structure of a Function

Similar to other programming languages, all functions consist of two sections: their header and their body. An example of the following can be found below:

function getOne() public pure returns(uint) {
    return 1; 
}

In the above, we have the code function getOne() public pure returns(uint) as the header of the function, while the code return 1; is the body of the function (the body of a function is always encapsulated by curly brackets).

Function Header

Focusing first on the header of a function, below is the required syntax that all function must have:

function <function_name>(<args>) <visibility>

In the parentheses, we list the parameters of the function. In addition to having a name, each parameter of a function must also be marked with its type. The only concept that might be new for most developers is the visibility of a function. In Solidity, we can mark a function with the following visibility traits:

• Public
• Private
• Internal
• External

Function Body

As of right now, the only thing we know what to do inside the body of a function is declaring/defining local variables. Inside the bodies of functions, we can also use regular mathematical operations like in other programming languages; the following code demonstrates this:

function getSquare(uint num) public returns(uint) {
    uint square = num ** 2;
    return square;
}