student_2.sol

//SPDX-License-Identifier: Unlicensed
pragma solidity >=0.8.0;

contract Student {
    struct student {
        uint256 prn;
        string name;
        string class;
        string department;
    }
    uint256 PRN;
    mapping(uint256 => student) studentMap;

    function addStudent(
        string memory name,
        string memory class,
        string memory department
    ) public {
        PRN += 1;
        studentMap[PRN] = student(PRN, name, class, department);
    }

    function getStudent(uint256 _id) public view returns (student memory) {
        return studentMap[_id];
    }

    function totalStudents() public view returns (uint256) {
        return (PRN);
    }

    fallback() external {
        addStudent("Unknown", "FE", "CSE");
    }
}