Write a program that calculates the sum   S = 1 + 2 + 3 + ... + N, where N is entered  by the user. Using the While loop.

******** In Algorithm ********
Algorithm
Variables i,S,N: integers
Begin
i ← 1 S ← 0
write("Enter an integer:")
read (N)
While ( i <= N )
S ← S + i
i ← i + 1
next
write("the sum 1+2+....+",N,"= ",S) End
End


Result : ==> Enter an integer : 6 the sum 1+2+....+6 = 21

******** In C ********

#include <stdio.h> int main(){ int i=1 , S=0 ,N; printf("Enter an integer :"); scanf ("%d",&N); while ( i <= N ) { S = S+i; i++ ; } printf("the sum 1+2+....+%d = %d\n",N,S); return 0; }

******** In C++ ********

#include <iostream> using namespace std; int main(){ int i=1 , S=0 ,N; cout<<"Enter an integer :"; cin>>N; while ( i <= N ){ S = S+i; i++ ; } cout<<"the sum 1+2+....+<<N<<" = "<<S; return 0; }

******** in Python ********

i=1 S=0 N = int(input("Enter N:")) while i <= N : S = S + i i = i + 1 print("the sum 1 +2+...+ N =:",S)

******** in JAVA ********
import java.util.Scanner;
class Main {
public static void main(String[] args){
Scanner sc = new Scanner (System.in);
System.out.print("Enter N :");
int N = sc.nextInt();
int i=1 , S=0; 
   while ( i <= N  ) {
        S = S+i;
        i++ ; 
   } 
System.out.print("the sum 1 ->"+N+"  =: "+S);
}
}

********* in C# *******

using System;
public class Ex15 {
public static void Main(string[] args)
{ int i=1 , S=0 ,N; 
   Console.Write("Enter N :");
   N=int.Parse(System.Console.ReadLine());
   while ( i <= N  ) {
        S = S+i;
        i++ ; 
   }
Console.Write("the sum 1+2+...+"+N+" = "+S);
}
}