Gas usage testing in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a gas variable initialized to zero.

Blockchain / Solidity

uint256 gasUsed = [1];

Drag options to blanks, or click blank then click option'

Agasleft()

B1

C0

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using gasleft() directly instead of zero

Initializing with 1 or 100

The gasUsed variable should start at zero to measure gas consumption properly.

2fill in blank

medium

Complete the code to record the starting gas before a function call.

Blockchain / Solidity

uint256 startGas = [1]();

Drag options to blanks, or click blank then click option'

Agasleft

BgasUsed

Cblock.gaslimit

Dgas

Attempts:

3 left

💡 Hint

Common Mistakes

Using gasUsed variable

Using block.gaslimit which is total gas limit

gasleft() returns the remaining gas at the current point in execution.

3fill in blank

hard

Fix the error in calculating gas used after function execution.

Blockchain / Solidity

gasUsed = startGas - [1]();

Drag options to blanks, or click blank then click option'

AgasUsed

Bblock.gaslimit

Cgasleft

Dgasleft()

Attempts:

3 left

💡 Hint

Common Mistakes

Using gasleft without parentheses

Using block.gaslimit incorrectly

gasleft() must be called as a function to get current gas left.

4fill in blank

hard

Fill both blanks to create a function that returns gas used by a call.

Blockchain / Solidity

function measureGas() public returns (uint256) {
    uint256 start = [1]();
    // some operation
    uint256 end = [2]();
    return start - end;
}

Drag options to blanks, or click blank then click option'

Agasleft

Bblock.timestamp

Cgasleft()

Dblock.number

Attempts:

3 left

💡 Hint

Common Mistakes

Using block.timestamp or block.number instead of gasleft()

Both start and end gas measurements use gasleft() function to get current gas left.

5fill in blank

hard

Fill all three blanks to create a gas measurement wrapper function.

Blockchain / Solidity

function gasWrapper() public returns (uint256) {
    uint256 [1] = [2]();
    performAction();
    uint256 gasUsed = [1] - [3]();
    return gasUsed;
}

Drag options to blanks, or click blank then click option'

AstartGas

Bgasleft

Cgasleft()

DendGas

Attempts:

3 left

💡 Hint

Common Mistakes

Using gasleft without parentheses

Using wrong variable names

We declare startGas variable, assign gasleft() at start, then subtract gasleft() after action.