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

Codes/Code-3.sol

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+// 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];
+    }
+}

Codes/Code-4.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.20;
+
+contract StudentData {
+    struct Student {
+        uint256 id;
+        string name;
+        uint8 age;
+        string course;
+    }
+
+    Student[] private students;
+
+    event StudentAdded(uint256 id, string name, string course);
+    event FallbackCalled(address sender, uint value, string message);
+
+    function addStudent(uint256 _id, string memory _name, uint8 _age, string memory _course) public {
+        students.push(Student(_id, _name, _age, _course));
+        emit StudentAdded(_id, _name, _course);
+    }
+
+    function getStudent(uint256 index) public view returns (uint256, string memory, uint8, string memory) {
+        require(index < students.length, "Invalid index");
+        Student memory s = students[index];
+        return (s.id, s.name, s.age, s.course);
+    }
+
+    function getTotalStudents() public view returns (uint256) {
+        return students.length;
+    }
+
+    fallback() external payable {
+        emit FallbackCalled(msg.sender, msg.value, "Fallback function triggered!");
+    }
+
+    receive() external payable {
+        emit FallbackCalled(msg.sender, msg.value, "Receive function triggered!");
+    }
+}