Let's use the loop to find the sum of integers
from `1`

to `100`

. To solve such a
problem, numbers are iterated over in loop and
their sum is sequentially written to some variable:

```
let res = 0;
for (let i = 1; i <= 100; i++) {
res = res + i;
}
console.log(res); // the required sum
```

You can simplify the solution
through the operator `+=`

:

```
let res = 0;
for (let i = 1; i <= 100; i++) {
res += i;
}
console.log(res);
```

Find the sum of even numbers
from `2`

to `100`

.

Find the sum of odd numbers
from `1`

to `99`

.

Find the product of integers
from `1`

to `20`

.