Binary Number Encryption/ Decryption in C++

 #include <iostream.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <process.h>	// for exit()
 #include <string.h>
 #include<conio.h>
 
 class data
 {
 	private:
 		char sid[20],bin[50];
 		int encr[50],decr[50];
 	
 	public:
 		int sum,ctr,bin_done; /*  Sum stores the number of binary values to get and ctr stores the index of encr[]  */
 		data();
 		void inputsid(); /* To input the Student ID */
 		void computenum(); /* To find the sum of last 5 digits of the Student Id */
 		void menu(); /* To print the menu */
 		void inputbin(); /* To input the Binary data */
 		void encrdata();  /* To encrypt the binary data */
 		void decrdata();  /* To decrypt the binary data */
 
 };
 		// Constructor to reset the counters
 		data::data()
 		{
 			sum=0;
 			ctr=0;
 			bin_done=0;
 		}
 //	  To Get the Student Id
 	   void data::inputsid()
 	   {
 			clrscr();
 			cout<<"Enter your Student ID Number: ";
 			gets(sid);
 			computenum();
 	   }
 
 //	  To compute the num of binary digits to enter
 	   void data::computenum()
 	   {
 			int num,s=0;
 			sum=0;
 			num=strlen(sid);
 			char str[6];
 			for(int i=num-5;i<=num;i++)
 			{
 				str[s]=sid[i];
 				s++;
 			}
 			int tmp=atoi(str);
 			while(tmp!=0)
 			{
 				sum+=tmp%10;
 				tmp/=10;
 			}
 		}
 
 //	  To print the main menu
 	   void data::menu()
 	   {
 //		 clrscr();
 		 cout<<"\n\n\n\n	 MENU\n";
 		 cout<<"1. Enter Data\n";
 		 cout<<"2. Encrypt Data\n";
 		 cout<<"3. Decrypt Data\n";
 		 cout<<"4. Exit\n";
 	   }
 
 	   //	  To get the binary Data
 	   void data::inputbin()
 	   {
 		 cout<<"Enter "<<sum<<" binary digits one character at a time: ";
 		 char tmp;
 		 for(int i=0;i<sum;)
 		 {
 		  cout<<"\nEnter character no "<<i+1<<":";
 		  cin>>tmp;
 		   if(tmp=='0' || tmp=='1')
 		   {
 			   bin[i]=tmp;
 			   i++;
 		   }
 		   else
 		   {
 			   cout<<tmp<<"\nInacceptable Value. Please enter 1 or 0 only";
 		   }
 		 }
 		 bin_done=1;
 		}
 
 //	  To Encrypt the data
 void data::encrdata()
 {
 	ctr=0;
 	int counter=0;
 	for(int i=0;i<sum;i++)
 	{
 		if(i==0)
 		{
 			if(bin[i]=='1')
 			{
 				encr[ctr]=counter;
 				ctr++;
 				counter++;
 			}
 			else
 			{
 				counter++;
 			}
 		}
 		else
 		{
 			if(bin[i]==bin[i-1])
 			{
 				counter++;
 			}
 			else
 			{
 				encr[ctr]=counter;
 				ctr++;
 				counter=1;
 			}
 		}
 	}
 	encr[ctr]=counter;
 	ctr++;
 	cout<<"\nThe Encrypted data is"<<ctr<<" : ";
 	for(i=0;i<ctr;i++)
 	{
 		cout<<encr[i];
 	}
 }
 
 //	  To Decrypt the data
 	   void data::decrdata()
 	   {
 		//int j=0;
 		 int val=0;
 
 		 cout<<"\nDecrypted data is: ";
 		 for(int i=0;i<ctr;i++)
 		 {
 		   for(int k=0;k<encr[i];k++)
 		   {
 		  //	 decr[j]=val;
 			   cout<<val;
 			//  j++;
 		   }
 		   if(val==0)
 		   {
 			   val=1;
 		   }
 		   else
 		   {
 			   val=0;
 		   }
 		 }
 	}
 
 void main()
 {
  data d;	/* Creating an object of the data class */
  d.sum=0;
  d.ctr=0;
  d.bin_done=0;
  char ch;
  clrscr();
  d.inputsid();
   
  do
  {
 	d.menu();
 	cout<<"\nENTER YOUR CHOICE:  ";
 	cin>>ch;
 	switch (ch)
 	{
 		case '1':
 		{
 			d.inputbin();
 			break;
 		}
 		case '2':
 		{
 			if(d.bin_done==0)
 			{
 				cout<<"Please enter the binary data first.";
 				getch();
 				break;
 			}
 			else
 			{			
 				d.encrdata();
 				break;
 			}
 		}
 		case '3':
 		{
 			if(d.ctr==0)
 			{
 				cout<<"Please encrypt the binary data first.";
 				getch();
 				break;
 			}
 			else
 			{
 				d.decrdata();
 				break;
 			}
 		}
 		case '4':
 		{
 			exit(0);
 			break;
 		}
 		default:
 			cout<<"Invalid choice";
 	}
 	getch();
   }while(1);
 }