Added code for practical 3 and 4, provided by Macho.

Codes/Code-3.sol

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.20;
+
+contract BankAccount {
+    mapping(address => uint256) private balances;
+
+    event Deposit(address indexed account, uint256 amount);
+    event Withdraw(address indexed account, uint256 amount);
+
+    function deposit() public payable {
+        require(msg.value > 0, "Deposit amount must be greater than 0");
+        balances[msg.sender] += msg.value;
+        emit Deposit(msg.sender, msg.value);
+    }
+
+    function withdraw(uint256 amount) public {
+        require(amount > 0, "Withdraw amount must be greater than 0");
+        require(balances[msg.sender] >= amount, "Insufficient balance");
+
+        balances[msg.sender] -= amount;
+        payable(msg.sender).transfer(amount);
+
+        emit Withdraw(msg.sender, amount);
+    }
+
+    function getBalance() public view returns (uint256) {
+        return balances[msg.sender];
+    }
+}