Sending Ether (transfer, send, call) in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send 1 ether using the transfer method.

Blockchain / Solidity

payable(msg.sender).[1](1 ether);

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

Acall

Bsend

CsendValue

Dtransfer

Attempts:

3 left

💡 Hint

Common Mistakes

Using send instead of transfer without checking return value.

The transfer method sends Ether and reverts on failure.

2fill in blank

medium

Complete the code to send 0.5 ether using the send method and check success.

Blockchain / Solidity

bool success = payable(receiver).[1](0.5 ether);

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Atransfer

Bcall

Csend

DsendValue

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking the boolean result of send.

The send method returns a boolean indicating success or failure.

3fill in blank

hard

Fix the error in sending Ether using call and check for success.

Blockchain / Solidity

(bool sent, ) = payable(receiver).[1]{value: amount}(''); require(sent, 'Failed to send Ether');

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

Acall

Btransfer

Csend

DsendValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using transfer or send with call syntax.

The call method is the recommended way to send Ether with gas forwarding and returns success status.

4fill in blank

hard

Fill both blanks to send Ether safely using call and handle failure.

Blockchain / Solidity

([1], ) = payable(receiver).[2]{value: msg.value}(''); require([1], 'Send failed');

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

Asent

Bsend

Ccall

Dtransfer

Attempts:

3 left

💡 Hint

Common Mistakes

Using transfer or send with call syntax.

Use call to send Ether and store the success boolean in sent.

5fill in blank

hard

Fill all three blanks to create a function that sends Ether using call and reverts on failure.

Blockchain / Solidity

function sendEther(address payable receiver) public payable { (bool [1], bytes memory [2]) = receiver.[3]{value: msg.value}(''); require([1], 'Failed to send Ether'); }

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

Asuccess

Bdata

Ccall

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using send or transfer instead of call in this pattern.

Use call to send Ether, capture success and data, and require success.

Practice

1.

Which Solidity function automatically reverts the transaction if sending Ether fails?

easy

A. approve

B. send

C. call

D. transfer

Solution

1. Step 1: Understand transfer behavior

   transfer sends Ether and automatically reverts if the transfer fails.

2. Step 2: Compare with other methods

   send returns false on failure without reverting; call requires manual check; approve is unrelated to sending Ether.

3. Final Answer:

   transfer -> Option D

4. Quick Check:

   Automatic revert on failure = transfer [OK]

Hint: transfer always reverts on failure, no manual check needed [OK]

Common Mistakes:

• Confusing send with transfer behavior
• Thinking call auto-reverts on failure
• Mixing approve with Ether sending

2.

Which of the following is the correct syntax to send 1 Ether using send in Solidity?

recipient.?{value: 1 ether}();

easy

A. send

B. transfer

C. call

D. approve

Solution

1. Step 1: Recall send syntax

   send is called as recipient.send{value: amount}() in Solidity 0.6+.

2. Step 2: Match syntax with options

   Only send matches send method usage for sending Ether.

3. Final Answer:

   send -> Option A

4. Quick Check:

   send syntax = recipient.send{value: 1 ether}() [OK]

Hint: send uses .send{value: amount}() syntax [OK]

Common Mistakes:

• Using transfer syntax with send
• Confusing call syntax with send
• Using approve which is unrelated

3.

What will be the output of the following Solidity code snippet?

bool success = recipient.send{value: 1 ether}();
if (!success) {
    revert("Send failed");
}

medium

A. Transaction reverts if send fails

B. Transaction always succeeds without revert

C. Compilation error due to syntax

D. Transaction succeeds but ignores failure

Solution

1. Step 1: Analyze send return value

   send returns false if sending Ether fails, but does not revert automatically.

2. Step 2: Check revert condition

   The code checks !success and calls revert manually, so transaction reverts on failure.

3. Final Answer:

   Transaction reverts if send fails -> Option A

4. Quick Check:

   send returns false + manual revert = revert on failure [OK]

Hint: send returns bool; revert manually on false [OK]

Common Mistakes:

• Assuming send auto-reverts
• Ignoring manual revert check
• Thinking code always succeeds

4.

Identify the error in this Solidity code snippet that uses call to send Ether:

(bool sent, ) = recipient.call{value: 1 ether}();
require(sent, "Failed to send Ether");

medium

A. Missing gas parameter in call

B. Incorrect syntax for call

C. No error; code is correct

D. Should use send instead of call

Solution

1. Step 1: Review call syntax

   The syntax recipient.call{value: 1 ether}() is correct for sending Ether with call.

2. Step 2: Check error handling

   The code checks sent boolean and reverts if false, which is proper error handling.

3. Final Answer:

   No error; code is correct -> Option C

4. Quick Check:

   call with value + require check = correct usage [OK]

Hint: call needs manual success check; this code does it [OK]

Common Mistakes:

• Thinking gas parameter is mandatory
• Confusing call syntax with send or transfer
• Ignoring manual success check

5.

You want to send Ether to a contract that might consume more than 2300 gas on fallback. Which method should you use to ensure the transfer succeeds?

hard

A. transfer

B. call

C. approve

D. send

Solution

1. Step 1: Understand gas limits of transfer and send

   transfer and send forward only 2300 gas, which may be insufficient for complex fallback functions.

2. Step 2: Use call for flexible gas forwarding

   call allows forwarding all available gas, ensuring the receiving contract can execute complex logic.

3. Final Answer:

   call -> Option B

4. Quick Check:

   call forwards all gas, suitable for complex fallback [OK]

Hint: Use call to forward all gas for complex fallback [OK]

Common Mistakes:

• Using transfer or send which limit gas to 2300
• Confusing approve with sending Ether
• Ignoring fallback gas requirements