Solidity Basics: Your First Lines of Code — Kudos board build (step 1/6)

GoalStart a tiny “KudosBoard” contract. Keep it lean: SPDX + pragma, one private string, and two functions to set and read a greeting. This compiles and deploys today.

Talk is cheap. Show me the code.

— Linus Torvalds

What to write

1. SPDX line
   add // SPDX-License-Identifier: MIT as the first line.
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   // SPDX-License-Identifier: MIT

   Declares the license in a machine-readable way. Most tooling and explorers expect this line; some compilers warn without it.

2. Pragma
   lock compiler with pragma solidity ^0.8.24;.
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   pragma solidity ^0.8.24;

   Pins a compiler range so builds and audits align. Prevents surprise behavior changes from newer compilers.

3. Contract shell
   contract KudosBoard { … } to scope everything.
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   contract KudosBoard {
       // ...
   }

   Defines the contract scope. Everything you write lives inside this block and becomes part of the ABI if marked public/external.

4. State
   string private _greeting; so the surface stays intentional.
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   string private _greeting;

   Private state forces callers through your functions. You control formatting, validation, and when changes are allowed.

5. Constructor
   accept a string and assign _greeting = greeting;.
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   constructor(string memory greeting) {
       _greeting = greeting;
   }

   Initializes storage at deploy time. Constructor args become part of the deploy transaction calldata.

6. Setter
   function setGreeting(string calldata greeting) external to update state.
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   function setGreeting(string calldata greeting) external {
       _greeting = greeting;
   }

   External means callable from outside; calldata avoids memory copies for inputs. This mutates storage and costs gas.

7. Getter
   function greeting() external view returns (string memory) to read it.
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   function greeting() external view returns (string memory) {
       return _greeting;
   }

   View marks it read-only; callers can read without gas when called locally. Returns a memory copy of the stored string.

Why SPDX/pragma lock license+compiler; private state keeps ABI intentional; explicit external/view + calldata reduce copies and make intent clear.

Try it Deploy this, call setGreeting(), then read greeting().

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract KudosBoard {
    string private _greeting;

    constructor(string memory greeting) {
        _greeting = greeting;
    }

    function setGreeting(string calldata greeting) external {
        _greeting = greeting;
    }

    function greeting() external view returns (string memory) {
        return _greeting;
    }
}

Next We’ll add per-user kudos and events in the following lessons.