I'm currently attempting to solve the Coinflip challenge by Ethernaut and I have trouble understanding the following line of code (after ==):

bool side = coinFlip == 1 ? true : false;

I can't seem to find any documentation on the syntax.

2 Answers 2


It's called the ternary operator: https://solidity.readthedocs.io/en/v0.4.24/miscellaneous.html?highlight=ternary

So in your example if coinFlip is equal to 1, side will be true, otherwise false.


The bool variable side is being assigned to the result of a ternary operator check.

It's listed in the miscellaneous section of the docs, and is basically the equivalent of

if (coinFlip == 1){ 
    return true;
    return false;

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