# Write a C++ program of sum of n natural number using loop

## Write a C++ program of sum of n natural number using loop

Given a number , write a program to find the sum of n natural numbers .

Sample input

`10`

Sample output:

`55`

## Write a C++ program of sum of n natural number using loop

The objective of the code is to find the sum of natural numbers up to n . Value of n is given by user .

Code(C++):-

Using For Loop:-

#include <iostream>
using namespace std;
int main()
{
int n,i,sum=0;
cout<<"Enter the number ";
cin>>n;
for(i=1;i<=n;i++)
{
sum=sum+i;
}
cout<<"sum is "<<sum;
return(0);
}

Output:-

Enter the number
10
sum is 55

Using While Loop:-

#include <iostream>
using namespace std;
int main()
{
int n,i=1,sum=0;
cout<<"Enter the number ";
cin>>n;
while(i<=n)
{
sum=sum+i;
i=i+1;
}
cout<<"sum is "<<sum;
return(0);
}

Output:-

Enter the number
10
sum is 55

Note :- Time complexity of these codes are O(n) but we can do this in O(1) by using a simple formula of sum of numbers up to n : check the code now

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