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contracts...sample.sol

//SPDX-License-Identifier: MIT

pragma solidity >=0.7.0 <0.9.0;

contract Sample{
    address public owner;
    uint256 serialNumber;

    struct Student{
        uint rollNo;
        string name;
        string dept;
    }

    mapping(address => Student) public students;

    constructor(){
        owner = msg.sender;
    }

    modifier isOwner(){
        require(owner == msg.sender,"Owner permission is not allowed");
        _;
    }

    function setSerialNumber(uint256 _serialnumber) external isOwner{
        serialNumber = _serialnumber;
    }

    function getSerialNumber() public view isOwner returns(uint256){
        return serialNumber;
    }

    function addStudent(uint _rollNo,string memory _name,string memory _dept)
    public
    {
        students[msg.sender] = Student(_rollNo,_name,_dept);
    }

    function getStudent(address _address) public isOwner view returns(Student memory){
        return students[_address];
    }


    function Factorial(uint _number) public pure returns(uint){
        uint fact = 1;
        for(uint i=0;i<=_number;i++){
            if(_number>0){
                fact = fact * _number;
                _number--;
            }
        }
        return fact;
       
    }

//string comparing...
  function compare(string memory str1,string memory str2) 
    public pure returns(bool)
    {
        if(bytes(str1).length!=bytes(str2).length){
            return false;
        }
        return keccak256(abi.encodePacked(str1)) == keccak256(abi.encodePacked(str2));
    }



}