Ethereum networks (mainnet, testnet) in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Ethereum networks (mainnet, testnet)

Start: Choose Network

↓

Use Testnet

Yes↓

Use Mainnet

↓

Deploy/Interact with Contracts

↓

Transactions Confirmed

↓

End

You pick a network: mainnet for real money or testnet for practice. Then you deploy or interact with contracts and wait for confirmations.

Execution Sample

Blockchain / Solidity

network = "testnet"
if network == "mainnet":
    print("Using real Ethereum network")
else:
    print("Using test network for practice")

This code chooses between mainnet and testnet and prints which network is used.

Execution Table

Step	Variable 'network'	Condition 'network == "mainnet"'	Branch Taken	Output
1	"testnet"	False	Else branch	"Using test network for practice"
2	-	-	-	Program ends

💡 Condition is false because network is 'testnet', so else branch runs and program ends.

Variable Tracker

Variable	Start	After Step 1	Final
network	undefined	"testnet"	"testnet"

Key Moments - 2 Insights

Why does the program print 'Using test network for practice' instead of 'Using real Ethereum network'?

Because the variable 'network' is set to 'testnet', the condition 'network == "mainnet"' is false (see execution_table step 1), so the else branch runs.

What is the difference between mainnet and testnet?

Mainnet is the real Ethereum network where real money is used. Testnet is a practice network with fake money to test code safely.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'network' at Step 1?

A "testnet"

B undefined

C "mainnet"

D "unknown"

💡 Hint

Check the 'Variable network' column in execution_table at Step 1.

At which step does the program decide to run the else branch?

A Step 2

B Program never runs else branch

C Step 1

D Before Step 1

💡 Hint

Look at the 'Branch Taken' column in execution_table.

If 'network' was set to 'mainnet', what would the output be?

A "Using test network for practice"

B "Using real Ethereum network"

C No output

D Error

💡 Hint

Think about the condition 'network == "mainnet"' and which branch runs.

Concept Snapshot

Ethereum networks:
- Mainnet: real Ethereum, real money
- Testnet: practice network, fake money
- Use 'if' to choose network
- Deploy/test contracts safely on testnet
- Switch to mainnet for real transactions

Full Transcript

This visual trace shows how a program chooses between Ethereum mainnet and testnet. The variable 'network' is set to 'testnet'. The program checks if 'network' equals 'mainnet'. Since it does not, it runs the else branch and prints 'Using test network for practice'. Mainnet is the real Ethereum network with real money. Testnet is a safe practice network with fake money. This helps developers test their code without risking real funds. The execution table tracks each step, showing variable values, conditions, branches, and output. The variable tracker shows how 'network' stays 'testnet'. Key moments clarify why the else branch runs and the difference between mainnet and testnet. The quiz asks about variable values and program flow to reinforce understanding.

Practice

1. Which Ethereum network should you use to test your smart contracts without risking real money?

easy

A. Private network

B. Mainnet

C. Testnet

D. Production network

Solution

1. Step 1: Understand the purpose of testnets

   Testnets are designed for testing and development without real value at risk.

2. Step 2: Compare with mainnet

   Mainnet is the live network where real transactions and value exist, so testing there risks real money.

3. Final Answer:

   Testnet -> Option C

4. Quick Check:

   Testnet = Safe testing network [OK]

Hint: Testnets are for safe practice, mainnet is for real use [OK]

Common Mistakes:

• Confusing mainnet with testnet
• Thinking private network is the default test environment
• Assuming production network is safe for testing

2. Which of the following is the correct way to specify the Ethereum mainnet network ID in your configuration?

easy

A. "networkId": 1

B. "networkId": 3

C. "networkId": 42

D. "networkId": 4

Solution

1. Step 1: Recall Ethereum network IDs

   Mainnet uses network ID 1, testnets have other IDs like 3 (Ropsten), 4 (Rinkeby), 42 (Kovan).

2. Step 2: Match the ID to mainnet

   Network ID 1 corresponds to the Ethereum mainnet.

3. Final Answer:

   "networkId": 1 -> Option A

4. Quick Check:

   Mainnet networkId = 1 [OK]

Hint: Mainnet always uses network ID 1 [OK]

Common Mistakes:

• Using testnet IDs for mainnet
• Confusing networkId with chainId
• Assuming networkId 0 is valid

3. Given the following code snippet to connect to an Ethereum network, what network will it connect to?

const provider = new ethers.providers.JsonRpcProvider("https://rinkeby.infura.io/v3/YOUR_PROJECT_ID");
const network = await provider.getNetwork();
console.log(network.name);

medium

A. "mainnet"

B. "rinkeby"

C. "ropsten"

D. "kovan"

Solution

1. Step 1: Identify the RPC URL

   The URL contains "rinkeby.infura.io", indicating the Rinkeby testnet.

2. Step 2: Understand provider.getNetwork()

   This method returns the network info based on the RPC URL, so it will return "rinkeby".

3. Final Answer:

   "rinkeby" -> Option B

4. Quick Check:

   RPC URL domain = rinkeby [OK]

Hint: Check the RPC URL domain for network name [OK]

Common Mistakes:

• Assuming default is mainnet
• Confusing testnet names
• Ignoring the URL and guessing

4. You wrote this code to deploy a contract on Ropsten testnet but get an error:

const provider = new ethers.providers.JsonRpcProvider("https://mainnet.infura.io/v3/YOUR_PROJECT_ID");
const signer = provider.getSigner();
// deploy contract code here

What is the main issue?

medium

A. Incorrect contract deployment syntax

B. Provider does not support getSigner()

C. Using mainnet RPC URL instead of Ropsten testnet URL

D. Missing private key for signer

Solution

1. Step 1: Examine the signer line

   JsonRpcProvider.getSigner() fails because public RPC providers like Infura do not expose signing accounts or private keys.

2. Step 2: Correct approach for deployment

   Create a wallet signer: const wallet = new ethers.Wallet('0x-your-private-key', provider); const signer = wallet.connect(provider);

3. Final Answer:

   Missing private key for signer -> Option D

4. Quick Check:

   Use Wallet(privateKey, provider) for signing [OK]

Hint: Use ethers.Wallet(privateKey, provider) for signing deployments [OK]

Common Mistakes:

• Using provider.getSigner() without wallet
• Assuming getSigner() works without wallet
• Overlooking private key requirement

5. You want to write a script that deploys a smart contract first on the Goerli testnet and then on the mainnet only if tests pass. Which approach correctly handles this?

hard

A. Deploy on Goerli testnet, run tests, then deploy on mainnet if tests pass

B. Deploy on mainnet first, then test on Goerli

C. Deploy simultaneously on both networks

D. Deploy only on mainnet and skip testnet

Solution

1. Step 1: Understand deployment best practices

   Testnets like Goerli are used to test contracts safely before mainnet deployment.

2. Step 2: Apply conditional deployment logic

   Deploy on Goerli, run tests, and only deploy on mainnet if tests succeed to avoid costly errors.

3. Final Answer:

   Deploy on Goerli testnet, run tests, then deploy on mainnet if tests pass -> Option A

4. Quick Check:

   Test on testnet before mainnet deployment [OK]

Hint: Test on Goerli first, then deploy mainnet if tests pass [OK]

Common Mistakes:

• Deploying on mainnet before testing
• Skipping testnets entirely
• Deploying on both networks at once