Ethereum Cookbook

assert()

1. Use assert() to prevent something bad from happening:

assert(condition);

2. Use it to check conditions such as integer overflow/underflow:

pragma solidity ^0.4.24;contract TestException {    function add(uint _a, uint _b) returns (uint) {       uint x = _a + _b;        assert(x > _b);        returns x;    }}

You should not use assert() blindly for checking overflow/underflow. It should be used only if you think that previous require or if checks would make it impossible.

3. Use it to check invariants in the contract. One example is to verify the contract balance against the total supply:

assert(address(this).balance >= totalSupply);

4. assert is commonly used to validate state after making changes. It helps in preventing conditions that should never be possible. ...