[Solidity] How to write if statements (conditional branching)?

This section explains how to write if statements (conditional branching) in Solidity.

Syntax

There are three patterns of if statements.

• if statement only (single condition)
• if - else (other condition)
• if - else if (other specific conditions)

Each is explained below.

A summary table is also provided for comparison operators (inequality signs used for conditional judgments).

if statement only (single condition)

The syntax for if statement only (single condition) is as follows.

// if the condition is true
if (condition) {
    Processing
}

if - else (other condition)

The syntax for if - else (other condition) is as follows.

// if the condition is true
if (condition) {
    Processing
// otherwise
} else {
    Processing
}

if - else if (other specific conditions)

The syntax for if - else if (other specific conditions) is as follows.

The “else if” clause can be repeated any number of times.

// if the condition is true
if (condition) {
    Processing
// otherwise (if the condition is true)
} else if (condition) {
    Processing
// otherwise (if the condition is true)
} else if (condition) {
    Processing
// otherwise
} else {
    Processing
}

Comparison Operators (inequality signs used for conditional judgments)

A table summarizing comparison operators is provided below.

Comparison Operator	Meaning
==	Equal
!=	Not equal
<	Less than
>	Greater than
<=	Less than or Equal to
>=	Greater than or Equal to

Sample Code

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Test {

    /* if statement only (single condition) */
    function checkAgeIf(uint8 age) public pure returns(string memory) {
        string memory message = "";
        // Under 18
        if (age < 18) {
            message = "Minors.";
        }

        return message;
    }

    /* if - else (other condition) */
    function checkAgeIfElse(uint8 age) public pure returns(string memory) {
        string memory message = "";
        // Under 18
        if (age < 18) {
            message = "Minors.";
        // Otherwise
        } else {
            message = "Adults.";
        }

        return message;
    }

    /* if - else if (other specific conditions) */
    function checkAgeIfElseIf(uint8 age) public pure returns(string memory) {
        string memory message = "";
        // Under 18
        if (age < 18) {
            message = "Minors.";
        // Under 20
        } else if (age < 20) {
            message = "Adults. Enjoy your last teenage years!";
        // Under 30
        } else if (age < 30) {
            message = "Adults. You are still in your twenties, young, young!";
        // Under 40
        } else if (age < 40) {
            message = "Adults. Your 30s will pass in the blink of an eye!";
        // Otherwise
        } else {
            message = "Adults. Let's stay healthy!";
        }

        return message;
    }
    
}