C++ Program to Calculate Sum of Natural Numbers (Using for loop)


This program is used to calculate the sum of the first ‘n’ natural numbers, where n is any value up to where the user wishes to calculate the sum.

To understand this program, you must have gone through the following concepts of C++ programming

1. for loop

2. operators

Go through the article on the ‘for’ loop written in the C++ language series to get a better understanding.

The positive numbers that start from 1 are known as Natural numbers.

The sum begins from 1 since natural numbers start from 1.



using namespace std;

int main()


int num;

// num is the value up to where the sum is calculated

cout<<"Enter a positive integer: ";


int sum=0;

for(int i=1;i<=num;i++)




cout<<"Sum: "<<sum;

return 0;





int num;

‘num’ is the variable declared to store the value up to where the user wishes to calculate the sum.

cout<<“Enter a positive integer: “;


Using cout and cin statements, we take input from the user.

int sum=0;

A new variable is declared and initialized with a 0 value to store the sum of natural numbers.

for (int i=1;i<=num;i++)

for loop starts here with iterator ‘i’. ‘i’ iterates from 1 to ‘num’, and in each iteration, the value of ‘i’ is added to the sum.


for i=1, sum=0


i++ updates the value of i to 2.

for i=2, sum=1


i++ updates the value of i to 3.

for i=3, sum=3


i++ updates the value of i to 4.

In this way, we get a final value containing the sum of natural numbers up to ‘num’



  • Barry Allen

    A Full Stack Developer with 10+ years of experience in different domain including SAP, Blockchain, AI and Web Development.


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