Return values in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Return values

Function called

↓

Execute function code

↓

Return value encountered

↓

Send value back to caller

↓

Caller receives value

↓

Use returned value

When a function runs, it does its work and then sends a value back to where it was called from.

Execution Sample

Blockchain / Solidity

function getBalance() {
  return 100;
}

let balance = getBalance();
console.log(balance);

This code defines a function that returns 100, then stores and prints that value.

Execution Table

Step	Action	Evaluation	Result
1	Call getBalance()	Function starts	Execution enters getBalance
2	Execute return 100	Return value 100	Function ends, returns 100
3	Assign returned value	balance = 100	Variable balance now 100
4	Print balance	console.log(100)	Output: 100
5	End	No more code	Program stops

💡 Function returns value 100, which is assigned and printed; program ends.

Variable Tracker

Variable	Start	After getBalance call	Final
balance	undefined	100	100

Key Moments - 2 Insights

Why does the function stop running after return?

Because return sends the value back and immediately ends the function, as shown in step 2 of the execution_table.

What happens to the returned value?

It goes back to the caller and can be stored or used, like balance = 100 in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value returned by getBalance() at step 2?

A undefined

B 100

C balance

D null

💡 Hint

Check the 'Evaluation' and 'Result' columns at step 2 in the execution_table.

At which step does the variable balance get its value?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column for when balance is assigned in the execution_table.

If the return statement was removed, what would happen to balance?

A balance would be undefined

B balance would be 100

C balance would be null

D balance would be NaN

💡 Hint

Without return, the function returns undefined by default; see variable_tracker for initial balance.

Concept Snapshot

Return values let a function send data back to where it was called.
Use 'return value;' inside the function.
After return, function stops running.
Caller can save or use the returned value.
Without return, functions return undefined by default.

Full Transcript

This visual trace shows how return values work in blockchain programming. When the function getBalance is called, it runs and hits the return statement which sends back the value 100. The function then stops running immediately. The caller receives this value and stores it in the variable balance. Finally, balance is printed to the console showing 100. Key points are that return ends the function and sends a value back, and the caller can use that value. If return is missing, the function returns undefined. This helps beginners see step-by-step how return values flow in code.

Practice

1.

What does the return statement do in a blockchain smart contract function?

easy

A. It sends a value back to the caller of the function.

B. It stops the contract from deploying.

C. It creates a new transaction on the blockchain.

D. It changes the contract's address.

Solution

1. Step 1: Understand the purpose of return

   The return statement is used inside a function to send a value back to whoever called the function.

2. Step 2: Identify what return does in blockchain functions

   In smart contracts, returning a value allows the caller to receive data from the function execution.

3. Final Answer:

   It sends a value back to the caller of the function. -> Option A

4. Quick Check:

   Return sends value back [OK]

Hint: Return sends data back to caller, not change contract [OK]

Common Mistakes:

• Thinking return creates transactions
• Confusing return with contract deployment
• Believing return changes contract address

2.

Which of the following is the correct syntax to specify a function that returns an uint in Solidity?

function getValue() _____ { return 42; }

easy

A. returns uint

B. return uint

C. return (uint)

D. returns (uint)

Solution

1. Step 1: Recall Solidity function return syntax

   In Solidity, the correct way to specify a return type is returns (type) after the function parentheses.

2. Step 2: Match the syntax with options

   returns (uint) uses returns (uint), which is the correct syntax.

3. Final Answer:

   returns (uint) -> Option D

4. Quick Check:

   Solidity uses returns (type) [OK]

Hint: Remember: returns keyword with parentheses for type [OK]

Common Mistakes:

• Omitting parentheses around type
• Using return instead of returns
• Placing return type inside function body

3.

What will be the output of this Solidity function call?

function multiply(uint a, uint b) public pure returns (uint) { return a * b; }

Calling multiply(3, 4) returns:

medium

A. 7

B. 12

C. 34

D. Error

Solution

1. Step 1: Understand the function logic

   The function multiplies two unsigned integers a and b and returns the product.

2. Step 2: Calculate the product of 3 and 4

   3 multiplied by 4 equals 12, so the function returns 12.

3. Final Answer:

   12 -> Option B

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Multiply inputs and return result [OK]

Common Mistakes:

• Adding instead of multiplying
• Concatenating numbers as strings
• Expecting syntax error

4.

Identify the error in this Solidity function that is supposed to return a bool:

function isEven(uint num) public pure returns (bool) { if (num % 2 == 0) { true; } else { false; } }

medium

A. Missing return statements before true and false.

B. The function should return uint instead of bool.

C. The modulus operator % is not allowed in Solidity.

D. The function should be marked as view instead of pure.

Solution

1. Step 1: Check the return statements

   The function uses true; and false; without return, so it does not actually return any value.

2. Step 2: Understand Solidity return requirements

   Every return value must be preceded by the return keyword to send the value back.

3. Final Answer:

   Missing return statements before true and false. -> Option A

4. Quick Check:

   Return keyword needed before values [OK]

Hint: Always use return before the value to send back [OK]

Common Mistakes:

• Omitting return keyword
• Confusing pure and view modifiers
• Thinking modulus operator is invalid

5.

You want to write a Solidity function that returns the sum of all elements in a uint[] array. Which of the following implementations correctly returns the sum?

function sumArray(uint[] memory arr) public pure returns (uint) { uint total = 0; for (uint i = 0; i < arr.length; i++) { total += arr[i]; } _____ }

hard

A. return arr.length;

B. return i;

C. return total;

D. return arr;

Solution

1. Step 1: Understand the function logic

   The function sums all elements in the array by adding each element to total.

2. Step 2: Identify the correct return value

   After the loop, the sum is stored in total, so returning total gives the correct sum.

3. Final Answer:

   return total; -> Option C

4. Quick Check:

   Return the sum variable total [OK]

Hint: Return the accumulator variable holding the sum [OK]

Common Mistakes:

• Returning array length instead of sum
• Returning loop index variable
• Returning the whole array instead of a value