First smart contract deployment in Blockchain / Solidity - Mini Project: Build & Apply

First smart contract deployment

📖 Scenario: You want to create a simple smart contract on the Ethereum blockchain that stores a number and allows you to update it.

🎯 Goal: Build and deploy a basic smart contract that stores a number and lets you change it.

📋 What You'll Learn

Create a smart contract named SimpleStorage

Add a state variable storedNumber of type uint

Write a function setNumber that updates storedNumber

Write a function getNumber that returns storedNumber

Deploy the contract and call getNumber to see the stored value

💡 Why This Matters

🌍 Real World

Smart contracts are programs that run on blockchains to automate agreements and store data securely.

💼 Career

Understanding how to write and deploy smart contracts is essential for blockchain developers and jobs in decentralized finance (DeFi) and NFTs.

1

Create the smart contract and state variable

Write a Solidity contract named SimpleStorage with a public state variable storedNumber of type uint initialized to 0.

Blockchain / Solidity

// Your code here

Hint

Start by declaring the contract and a public unsigned integer variable initialized to zero.

2

Add a function to update the stored number

Inside the SimpleStorage contract, add a public function named setNumber that takes a uint parameter called newNumber and sets storedNumber to newNumber.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint public storedNumber = 0;

    // Your code here
}

Hint

Write a function that takes a number and updates the storedNumber variable.

3

Add a function to read the stored number

Inside the SimpleStorage contract, add a public view function named getNumber that returns a uint and returns the value of storedNumber.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint public storedNumber = 0;

    function setNumber(uint newNumber) public {
        storedNumber = newNumber;
    }

    // Your code here
}

Hint

Create a function that returns the current stored number without changing state.

4

Deploy and test the contract

Deploy the SimpleStorage contract on a test network or local blockchain. Then call setNumber(42) and afterwards call getNumber() to print the stored number.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint public storedNumber = 0;

    function setNumber(uint newNumber) public {
        storedNumber = newNumber;
    }

    function getNumber() public view returns (uint) {
        return storedNumber;
    }
}

// After deployment, call setNumber(42) and then getNumber() to see the result
// Your code here

Hint

Use Remix IDE or a local blockchain like Hardhat to deploy and test your contract. Call setNumber(42) then getNumber() to see 42.

Practice

1. What does deploying a smart contract mean in blockchain?

easy

A. Testing the contract on a local computer only

B. Making the contract code live and usable on the blockchain

C. Writing the contract code in a text editor

D. Deleting the contract from the blockchain

Solution

1. Step 1: Understand deployment meaning

   Deployment means putting the contract code on the blockchain so it can run.

2. Step 2: Differentiate from writing and testing

   Writing is coding, testing is checking locally or on test networks, deployment is live on blockchain.

3. Final Answer:

   Making the contract code live and usable on the blockchain -> Option B

4. Quick Check:

   Deploy = live on blockchain [OK]

Hint: Deployment means contract is live on blockchain [OK]

Common Mistakes:

• Confusing deployment with just writing code
• Thinking testing is deployment
• Believing deployment deletes contracts

2. Which of the following is the correct Solidity syntax to start a simple contract named MyContract?

easy

A. contract MyContract { }

B. class MyContract { }

C. function MyContract() { }

D. contract = MyContract()

Solution

1. Step 1: Recall Solidity contract declaration

   Solidity uses the keyword contract followed by the contract name and braces.

2. Step 2: Check each option's syntax

   contract MyContract { } matches Solidity syntax; others use wrong keywords or formats.

3. Final Answer:

   contract MyContract { } -> Option A

4. Quick Check:

   Solidity contract starts with 'contract' keyword [OK]

Hint: Solidity contracts start with 'contract' keyword [OK]

Common Mistakes:

• Using 'class' instead of 'contract'
• Writing function instead of contract
• Assigning contract like a variable

3. Given this Solidity contract snippet deployed on a test network:

contract Counter {
  uint count = 0;
  function increment() public {
    count += 1;
  }
  function getCount() public view returns (uint) {
    return count;
  }
}

If you call increment() twice and then getCount(), what is the output?

medium

A. 0

B. 1

C. 2

D. Error: function not found

Solution

1. Step 1: Understand contract state changes

   Each call to increment() adds 1 to count, starting from 0.

2. Step 2: Calculate after two increments

   After two calls, count becomes 2. getCount() returns this value.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   2 increments = count 2 [OK]

Hint: Each increment adds 1; two increments mean count is 2 [OK]

Common Mistakes:

• Forgetting state changes persist on blockchain
• Assuming count resets each call
• Confusing function names

4. You try to deploy this Solidity contract but get a syntax error:

contract Simple {
  uint number
  function setNumber(uint num) public {
    number = num;
  }
}

What is the cause of the error?

medium

A. Missing return type in function

B. Function setNumber must be private

C. Contract name must be lowercase

D. Missing semicolon after uint number

Solution

1. Step 1: Check Solidity syntax rules

   Variable declarations require a semicolon at the end.

2. Step 2: Identify missing semicolon

   uint number line misses a semicolon, causing syntax error.

3. Final Answer:

   Missing semicolon after uint number -> Option D

4. Quick Check:

   Missing semicolon = syntax error [OK]

Hint: Check semicolons after variable declarations [OK]

Common Mistakes:

• Thinking function visibility causes syntax error
• Believing contract names must be lowercase
• Expecting return type for void functions

5. You want to deploy a smart contract that stores user names and their balances. Which approach is best to deploy and test it safely before using real money?

hard

A. Deploy on a test network like Ropsten or Goerli first

B. Deploy directly on the main Ethereum network

C. Write the contract but never deploy it

D. Deploy on a private computer without blockchain

Solution

1. Step 1: Understand deployment environments

   Mainnet uses real money; testnets simulate blockchain without real cost.

2. Step 2: Choose safe testing method

   Deploying on testnets like Ropsten or Goerli lets you test without risking real funds.

3. Final Answer:

   Deploy on a test network like Ropsten or Goerli first -> Option A

4. Quick Check:

   Testnet deployment = safe testing [OK]

Hint: Use test networks to avoid losing real money [OK]

Common Mistakes:

• Deploying directly on mainnet without testing
• Not deploying at all and missing testing
• Using private computer without blockchain for deployment