Whats the best way to find the execution cost of a function

Question

I am interested to analyze the execution cost of the function by considering the best practice to adopt, because of that I used bytes32 rather than String which decrease the execution cost of the function from infinite to finite.

I am eager to know whats the best way to find the accurate gas execution cost. I compile the same code 2-3 times in remix and sometimes it gives me the different execution gas cost. Like for below function sometimes it gives me

    Execution cost: 624gas 

and sometimes

    Execution cost: 454 gas.

The function is below which simply return the length of an array.

    function totalLoans() public view returns (uint){
    return(allLoansData.length);
    }

1) Does the difficulty parameter also impact the execution gas cost? 2) Is there any way that we find the ideal gas cost?

Answer 1

The gas cost for the same function may be different depending on the state of the contract. I had asked a question here which will give you an idea on what factors gas depends on.

The best way I know to estimate Gas is to use estimate gas method. Since extra gas is returned in most cases ( not when tx fails because of assert statement), it is advised to send higher gas price than estimated. Extra gas send will be refunded.