Accumulation in the loop

Inside the loops, in addition to printing pages, you can also use standard mathematical operations. For example, addition:

for (var i = 1; i <= 5; i++) {
  console.log(2 + 2);
}

The result of the program will be the following:

LOG: 4 (number)
LOG: 4 (number)
LOG: 4 (number)
LOG: 4 (number)
LOG: 4 (number)

Number 4 will be logged in the console 5 times, because this is how many iterations this loop has. That is, at each iteration, twos will be added and logged in the console. But if at each iteration we need to get a new, increased, number, we must act differently. We need to create one more variable before the loop, which will store the sum:

var sum = 0;

for (var i = 1; i <= 5; i++) {
  sum += 2;
  console.log(sum);
}

The program will log:

LOG: 2 (number)
LOG: 4 (number)
LOG: 6 (number)
LOG: 8 (number)
LOG: 10 (number)

Each iteration adds 2 to sum, building up a running total. We declare and initialize sum before the loop, rather than inside its body. This is important: its value then carries over between iterations instead of being reset to zero each time.

This operation is called accumulation of a value in the loop.

Let’s practice accumulating values ​​and calculate the sum of numbers from 1 to 10. We will log intermediate results in the console to monitor the changes in the sum.