C++ Program to find the sum of n natural numbers

Numbers 1, 2, 3, …., n are known as natural numbers. This program takes the value of n and finds the sum of first n natural numbers.
For example, If user enters 5 as the value of n then the sum of first n(n=5) natural numbers would be:
1+2+3+4+5 = 15

Example: Program to calculate the sum of n natural numbers

To understand this program you should have the knowledge of C++ while loop.

#include
using namespace std;
int main(){
   int n, sum=0;
   cout<<"Enter the value of n(should be a positive integer): "; 
   //Storing the input integer value into the variable n
   cin>>n;

   /* If user enters value of n as negative then display an 
    * error message to user that the value of n is invalid 
    */
   if(n<=0){
      cout<<"Invalid value of n";
   }
   else{
      // We are using while loop to calculate the sum
     int i=1;
     while(i<=n){
	 sum=sum+i;
	 i++;
     }
     cout<<"Sum of first n natural numbers is: "<<sum;
   }

   return 0;
}

Output:

Enter the value of n(should be a positive integer): 5
Sum of first n natural numbers is: 15

You can also use for loop for this program. You just need to replace this part:

int i=1;  
while(i<=n){ 
      sum=sum+i;  
      i++;   
}

with this:

for(int i = 1; i <= n; i++) {
   sum = sum+i;
}

We can solve this problem using recursion as well, you can find the program here: Program to find the sum of n natural numbers using recursion.