Merge pull request #83 from 0xSandyy/Divide-By-Zero

Divide by zero vulnerability added to DoS revert.

vulnerabilities/dos-revert.md

@@ -87,6 +87,14 @@ It's important to take caution in enforcing expected contract balances of tokens
 
 Consider, for example, a contract which expects the Ether balance to be 0 for the first deposit to allow for custom accounting logic. An attacker may forcibly send Ether to the contract before the first deposit, causing all deposits to revert. 
 
+### Divide by Zero
+In solidity if the contract attempts to perform division when the denominator is ``zero``, the call reverts. Thus, the denominator should be always checked before division to prevent DoS revert.
+```solidity
+function foo(uint num, uint den) public pure returns(uint result) {
+  result = num / den; // if den = 0, the execution reverts
+}
+```
+
 ### Sources
 
 - https://consensys.github.io/smart-contract-best-practices/attacks/denial-of-service/