The positive integers **1, 2, 3, ...** are known as natural numbers.

## Example 1: Sum of Natural Numbers using for Loop

```
// program to display the sum of natural numbers
// take input from the user
let number = parseInt(prompt('Enter a positive integer: '));
let sum = 0;
// looping from i = 1 to number
// in each iteration, i is increased by 1
for (let i = 1; i <= number; i++) {
sum += i;
}
console.log('The sum of natural numbers:', sum);
```

**Output**

Enter a positive integer: 100 The sum of natural numbers: 5050

In the above program, the user is prompted to enter a number.

The `parseInt()`

converts the numeric string value to an integer value.

The `for`

loop is used to find the sum of natural numbers up to the number provided by the user.

- The value of
`sum`is**0**initially. - Then, a
`for`

loop is used to iterate from`i = 1 to 100`

. - In each iteration,
`i`is added to`sum`and the value of`i`

is increased by**1**. - When
`i`becomes**101**, the test condition is`false`

and`sum`will be equal to`0 + 1 + 2 + ... + 100`.

## Example 2: Sum of Natural Numbers using while Loop

```
// program to display the sum of natural numbers
// take input from the user
let number = parseInt(prompt('Enter a positive integer: '));
let sum = 0, i = 1;
// looping from i = 1 to number
while(i <= number) {
sum += i;
i++;
}
console.log('The sum of natural numbers:', sum);
```

**Output**

Enter a positive integer: 100 The sum of natural numbers: 5050

In the above program, the user is prompted to enter a number.

The `while`

loop is used to find the sum of natural numbers.

- The
`while`

loop continues until the number is less than or equal to**100**. - During each iteration,
`i`is added to the`sum`

variable and the value of`i`is increased by**1**. - When
`i`becomes**101**, the test condition is`false`

and`sum`will be equal to`0 + 1 + 2 + ... + 100`.