C++ Program to Find and Print the Sum of First n Natural Numbers

This article is created to provide some programs in C++ that find and print the sum of the first n natural numbers. The value n must be entered by the user at run-time. The program is created in the following ways:

• Find and print the sum of first n natural numbers using the while loop
• Find and print the sum of first n natural numbers using a for loop
• Find and print the sum of first n natural numbers using a user-defined function

Note: A natural number starts with 1 and continues like 1, 2, 3,...

Find the sum of first n natural numbers using the while loop

The question is: write a program in C++ that receives the value of n and prints the sum of the first n natural numbers. Here is its answer:

#include<iostream>
using namespace std;

int main()
{
   int n, natural=1, sum=0;
   cout<<"Enter the Value of n: ";
   cin>>n;
   while(natural<=n)
   {
      sum = sum+natural;
      natural++;
   }
   cout<<"\nSum of First "<<n<<" Natural Numbers = "<<sum;
   cout<<endl;
   return 0;
}

Here is the initial output produced by the above C++ program on finding and printing the sum of n natural numbers:

Now supply the number, say 10, as the value of n and press the ENTER key to find the sum of the first 10 natural numbers, as shown in the snapshot given below:

Find the sum of first n natural numbers using the for loop

This program is created using the for loop instead of while.

#include<iostream>
using namespace std;

int main()
{
   int n, natural, sum=0;
   cout<<"Enter the Value of n: ";
   cin>>n;
   for(natural=1; natural<=n; natural++)
      sum = sum+natural;
   cout<<"\nSum of First "<<n<<" Natural Numbers = "<<sum;
   cout<<endl;
   return 0;
}

Here is its sample run with user input: 12.

Find the sum of first n natural numbers using function

This is the last program created using a user-defined function named myfun() that takes an integer, say n, as its argument and then finds and returns the sum of the first n natural numbers.

#include<iostream>
using namespace std;

int myfun(int);
int main()
{
   int n, sum;
   cout<<"Enter the Value of n: ";
   cin>>n;
   sum = myfun(n);
   cout<<"\nSum of First "<<n<<" Natural Numbers = "<<sum;
   cout<<endl;
   return 0;
}
int myfun(int n)
{
   int natural, sum=0;
   for(natural=1; natural<=n; natural++)
      sum += natural;
   return sum;
}

C++ Quiz