How a for loop works? How to use it in your program?

The for loop is used to repeat some instructions a determinate number of times. The for loop is really useful for repetitive action, such as blinking a led or move a servomotor from 0° to 180°.

for (initialization; condition; incrementation) {
  // Your program

As we can see, the for loop takes in parameters an initializing, a condition for which the loop is executed while the condition is true and an incrementation. A variable can be used in the loop which is initialized at a number and increment it every loop until the condition is false.

The incrementation is called the step. This is the value which your variable will be increment.

How to write this condition?

The for condition can be difficult to write with all the operators that exist!

We wrote a course about all the operators you can use in a for loop.

We will few examples of for loop below:

for (int i = 0; i < 255; i++) {
    Serial.println(i);//Your program

As we can see in our example, we use an i variable which is initialized at 0 and execute 255 times our instructions inside loop. The step is corresponds to i++, that ‘s mean that at each loop we will add 1 to variable i.

Nevertheless you can change the step that the loop finish quicker without executing 255 times. You can write for example i+=2 instead of i++. In this case the loop will execute 128 times.

Beware of how many times your loop will be executed!

If we use the previous example, the first value of i is 0 but it’s last value will be 254 et not 255 because we wrote lower (<) and not lower or equal (<=). I you change by lower or equal the condition of your loop you will have 256 steps in your loop because it will be from 0 to 255.


  • For loop with decreasing incrementation

We will see now how to do a for loop in which the incrementation of the  variable is decreasing.

for (int i = 255; i > 0; i--) {
    Serial.println(i);// Your program

In this example we can see that the variable i goes from 255 to 1. The step is i– which mean at each loop the variable decrease of one.