write a cpp program to calculate sum of first n natural numbers

1// Method 1: Mathematical -> Sum up numbers from 1 to n 
2int sum(int n){
3	return (n * (n+1)) / 2;
4}
5
6// Method 2: Using a for-loop -> Sum up numbers from 1 to n 
7int sum(int n){
8	int tempSum = 0; 
9  	for (int i = n; i > 0; i--){
10     	tempSum += i;  
11    }
12  	return tempSum; 
13}
14
15// Method 3: Using recursion -> Sum up numbers from 1 to n 
16int sum(int n){
17	return n > 0 ? n + sum(n-1) : 0; 
18}

1
2#include <iostream>
3
4using namespace std;
5
6int main(){
7	int N,i,sum=0;
8	cin>>N;
9     for(i=0;i<=N;)
10     {
11         sum=sum+N;
12        N--;
13     }
14     cout<<sum;
15}
16