Program Sum of Even Numbers 1 To N

Easyway how to write C++ Programs sum all even numbers from 1 to N

/*
Write a C++ Program to display and sum of All Even numbers from
1 to n (the entered positive number)by FOR Loop

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*/
#include<iostream.h>

#include<conio.h>

void main()
{

  clrscr();

  int number, counter;
  long sum = 0;
  cout<<"\n Enter a positive number = ";

  cin>>number;

  cout<<"\n\n ----------- Results ------------";

  cout<<"\n\n All Even Numbers between \n 1 to n(entered positive number)\n by For Loop ";

  for (counter = 2; counter <= number; counter+=2)
           {
           cout<<"\n \t"<<counter;
           sum = sum + counter;
           }
  cout<<"\n\n The Sum of All Even Numbers between \n 1 to n(entered positive number)\n by For Loop ="<<sum;

  getch();

}