# Lesson 3: Outline

## Lesson 3: Functions and Modifiers in Solidity

**Objective:** To understand how to write and use functions in Solidity, and to learn about function modifiers for enforcing certain conditions and managing access control in smart contracts.

### **Part 1: Functions in Solidity**

* **Function Declaration and Types**:
  * Understand the syntax for declaring functions.
  * Different types of functions: `public`, `private`, `internal`, and `external`.
* **Return Values and Visibility**:
  * How to define return values for functions.
  * Understand the implications of function visibility.
* **Function Modifiers**:
  * Usage of `view`, `pure`, and state-changing functions.
* **Function Parameters**:
  * Passing parameters to functions.
  * Using `memory` and `storage` keywords for complex data types.
* **Example: Creating a Function**

  ```solidity
  pragma solidity ^0.8.0;

  contract MyContract {
      uint public count = 0;

      function increment() public {
          count += 1;
      }

      function getCount() public view returns (uint) {
          return count;
      }
  }
  ```

### **Part 2: Modifiers in Solidity**

* **Understanding Modifiers**:
  * Purpose of modifiers in Solidity.
  * Writing custom modifiers to enforce conditions.
* **Common Use Cases**:
  * Restricting access to certain functions.
  * Validating inputs or conditions before executing function logic.
* **Example: Using a Modifier**

  ```solidity
  pragma solidity ^0.8.0;

  contract MyContract {
      address public owner;

      constructor() {
          owner = msg.sender;
      }

      modifier onlyOwner() {
          require(msg.sender == owner, "Not the owner");
          _;
      }

      function changeOwner(address newOwner) public onlyOwner {
          owner = newOwner;
      }
  }
  ```