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In this program, you will learn how to use the for loop and while loop in Java to calculate the sum of natural numbers. To understand this example, you need to be familiar with the following Java programming concepts:

- Java for Loop
- Java while and do…while Loop

Positive numbers such as 1, 2, 3… are known as natural numbers, and their sum is the result of all numbers beginning with 1 and ending with the given number.

For n, the sum of natural numbers is:

1 + 2 + 3 + ... + n

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**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:

**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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