The positive numbers 1, 2, 3... are known as natural numbers and its sum is the result of all numbers starting from 1 to the given number.

For n, the sum of natural numbers is:

1 + 2 + 3 + ... + n

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

```
public class SumNatural {
public static void main(String[] args) {
int num = 100, sum = 0;
for(int i = 1; i <= num; ++i)
{
// sum = sum + i;
sum += i;
}
System.out.println("Sum = " + sum);
}
}
```

**Output**

Sum = 5050

The above program loops from 1 to the given `num`(100) and adds all numbers to the variable `sum`.

You can solve this problem using a while loop as follows:

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

```
public class SumNatural {
public static void main(String[] args) {
int num = 50, i = 1, sum = 0;
while(i <= num)
{
sum += i;
i++;
}
System.out.println("Sum = " + sum);
}
}
```

**Output**

Sum = 1275

In the above program, unlike a for loop, we have to increment the value of `i` inside the body of the loop.

Though both programs are technically correct, it is better to use for loop in this case. It's because the number of iteration (up to `num`) is known.

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