saving 6 gas it iszero()

saving_gas/README.md

@@ -9,6 +9,13 @@
 - avoid calls to other contracts.
 - ++i uses 5 gas less than i++.
 - if you don’t need a variable anymore, you should delete it using the delete keyword provided by solidity or by setting it to its default value.
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+<img width="532" alt="Screen Shot 2023-01-24 at 4 28 45 PM" src="https://user-images.githubusercontent.com/1130416/214452718-b051caed-49e4-45fb-b955-976d20e97cbd.png">
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 <br>
 
 #### pack variables