Why gas efficiency saves money in Blockchain / Solidity - Visual Breakdown

Concept Flow - Why gas efficiency saves money

User sends transaction

↓

Transaction uses gas units

↓

Gas price set by network

↓

Total cost = gas units * gas price

↓

User pays total cost in cryptocurrency

↓

More efficient code uses fewer gas units

↓

Lower total cost for user

This flow shows how a blockchain transaction costs money based on gas units used and gas price, so using less gas saves money.

Execution Sample

Blockchain / Solidity

function transfer() public pure returns (uint) {
  uint gasUsed = 21000; // simple transfer
  uint gasPrice = 50; // gwei
  uint cost = gasUsed * gasPrice;
  return cost;
}

Calculates cost of a simple blockchain transfer by multiplying gas used by gas price.

Execution Table

Step	Gas Used	Gas Price (gwei)	Calculation	Cost (gwei)
1	21000	50	21000 * 50	1050000
2	15000	50	15000 * 50	750000
3	10000	50	10000 * 50	500000
Exit	-	-	-	Calculation complete

💡 Cost calculated for different gas usages; lower gas used means lower cost.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
gasUsed	undefined	21000	15000	10000	10000
gasPrice	undefined	50	50	50	50
cost	undefined	1050000	750000	500000	500000

Key Moments - 2 Insights

Why does using less gas reduce the cost?

Because cost is gasUsed multiplied by gasPrice, so lowering gasUsed directly lowers total cost, as shown in execution_table rows 1 to 3.

Does changing gasPrice affect cost the same way as gasUsed?

Yes, cost depends on both gasUsed and gasPrice, but in this example gasPrice stays constant to show effect of gasUsed changes (see variable_tracker).

Visual Quiz - 3 Questions

Look at the execution_table, what is the cost when gasUsed is 15000?

A 1050000 gwei

B 750000 gwei

C 500000 gwei

D 15000 gwei

💡 Hint

Check execution_table row 2 under Cost column.

At which step does the cost become 500000 gwei?

A Step 3

B Step 1

C Step 2

D Exit

💡 Hint

Look at execution_table rows and find where Cost is 500000.

If gasPrice doubled to 100 gwei but gasUsed stayed 21000, what would cost be?

A 1050000 gwei

B 420000 gwei

C 2100000 gwei

D 500000 gwei

💡 Hint

Multiply gasUsed 21000 by new gasPrice 100.

Concept Snapshot

Gas cost = gasUsed * gasPrice
Lower gasUsed means lower cost
Gas price is set by network
Efficient code uses less gas
Saves money on blockchain transactions

Full Transcript

When you send a blockchain transaction, it uses gas units. The network sets a gas price. Your total cost is gas units times gas price. Using less gas means you pay less. For example, a simple transfer uses 21000 gas units. If gas price is 50 gwei, cost is 21000 times 50 equals 1050000 gwei. If you optimize code to use 15000 gas units, cost drops to 750000 gwei. This shows why gas efficiency saves money.

Practice

1. Why does gas efficiency matter when writing blockchain smart contracts?

easy

A. Because it makes the code run faster on a regular computer

B. Because it increases the size of the blockchain

C. Because it reduces the transaction cost paid in cryptocurrency

D. Because it allows unlimited transactions without fees

Solution

1. Step 1: Understand what gas represents in blockchain

   Gas is a fee paid to execute operations on the blockchain, measured in cryptocurrency.

2. Step 2: Connect gas efficiency to cost savings

   Using less gas means paying less cryptocurrency for the same operation.

3. Final Answer:

   Because it reduces the transaction cost paid in cryptocurrency -> Option C

4. Quick Check:

   Gas efficiency = lower transaction cost [OK]

Hint: Gas means fee; less gas means less money spent [OK]

Common Mistakes:

• Confusing gas with code speed on a computer
• Thinking gas increases blockchain size
• Believing gas allows free transactions

2. Which of the following Solidity code snippets is more gas efficient?

easy

A. Using for loops with large fixed ranges

B. Using string for storing numbers

C. Using multiple require statements instead of one

D. Using uint8 instead of uint256 for small numbers

Solution

1. Step 1: Identify data types and their gas costs

   Smaller data types like uint8 use less storage and gas than larger types like uint256.

2. Step 2: Compare options for gas efficiency

   Using uint8 for small numbers saves gas compared to storing numbers as strings or using inefficient loops.

3. Final Answer:

   Using uint8 instead of uint256 for small numbers -> Option D

4. Quick Check:

   Smaller data types = less gas [OK]

Hint: Use smallest suitable data type to save gas [OK]

Common Mistakes:

• Using strings to store numbers wastes gas
• Multiple require statements add unnecessary gas
• Large loops increase gas cost

3. Consider this Solidity function:

function add(uint256 a, uint256 b) public pure returns (uint256) {
    uint256 c = a + b;
    return c;
}

If you replace uint256 with uint8 for variables a, b, and c, what is the main effect on gas usage?

medium

A. Gas usage will decrease because smaller types use less storage

B. Gas usage will increase because smaller types are slower

C. Gas usage will stay the same because addition cost is fixed

D. Gas usage will cause an error due to overflow

Solution

1. Step 1: Understand gas cost of data types

   Smaller data types like uint8 use less gas for storage and operations than uint256.

2. Step 2: Consider the effect on gas usage

   Replacing uint256 with uint8 reduces gas because less storage and computation is needed.

3. Final Answer:

   Gas usage will decrease because smaller types use less storage -> Option A

4. Quick Check:

   Smaller type = less gas [OK]

Hint: Smaller integer types reduce gas cost [OK]

Common Mistakes:

• Assuming smaller types slow down code
• Ignoring gas savings from smaller storage
• Confusing overflow errors with gas usage

4. This Solidity function is intended to save gas by using uint8 but causes an error:

function multiply(uint8 a, uint8 b) public pure returns (uint8) {
    uint8 result = a * b;
    require(result >= a, "Overflow");
    return result;
}

What is the main problem causing the error?

medium

A. Using uint8 causes syntax errors

B. The require condition does not correctly detect overflow

C. Multiplication is not allowed on uint8

D. The function should return uint256 instead

Solution

1. Step 1: Analyze the overflow check logic

   The condition result >= a is not a reliable way to detect overflow in multiplication.

2. Step 2: Understand why this causes errors

   If overflow occurs, the check might pass incorrectly or fail, causing unexpected errors.

3. Final Answer:

   The require condition does not correctly detect overflow -> Option B

4. Quick Check:

   Incorrect overflow check causes errors [OK]

Hint: Use safe math libraries for overflow checks [OK]

Common Mistakes:

• Assuming uint8 causes syntax errors
• Believing multiplication is disallowed on uint8
• Ignoring overflow risks in small types

5. You want to optimize a smart contract function that stores user balances. Which approach saves the most gas and money?

hard

A. Use mapping(address => uint8) if balances never exceed 255

B. Store balances as strings to allow flexible formatting

C. Store balances as uint256 and update them frequently

D. Use arrays to store balances and loop through them on each update

Solution

1. Step 1: Identify the best data structure and type for gas efficiency

   Using a mapping with uint8 saves gas by using less storage and avoiding loops.

2. Step 2: Compare other options for gas cost

   Using uint256 wastes storage if values are small; strings and arrays increase gas due to size and looping.

3. Final Answer:

   Use mapping(address => uint8) if balances never exceed 255 -> Option A

4. Quick Check:

   Smaller types + mappings = gas savings [OK]

Hint: Use smallest type and mappings to save gas [OK]

Common Mistakes:

• Using large types unnecessarily wastes gas
• Storing numbers as strings is inefficient
• Looping over arrays increases gas cost