How Do I Update A Record Using Input Output Stream In C++

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

class record
{
public:
	int studentmarks[3];
	string studentname[3];
	int marks[3];
	
	void studentinfo()
	{
		ifstream input;
	input.open("save.txt");
	ofstream output;
	output.open("show.xls");

	string line;

	if(input.is_open())
	{
		while (getline(input,line))
		{
          
			output<<line<<endl;

		}


    }



	}


	void info()
	{
		ofstream myfile;
		myfile.open("save.txt");

		for(int i= 0; i<3; i++)
		{
         cout<<"Enter the name of students"<<endl;
		 getline(cin,studentname[i]);

        }

	for(int i= 0; i<3; i++)
		{
         cout<<"Enter the marks of students"<<endl;
		 cin>>studentmarks[i];

        }


	myfile<<"Name"<<"\t"<<"Marks"<<endl;
	for(int i =0; i<3; i++)
	{

		myfile<<studentname[i]<<"\t"<<studentmarks[i]<<endl;


	} 













	}


private:

};

int main()
{
	

	

	record c;
	c.info();

	c.studentinfo();

	
	system("pause");









}