---
title: for
categories: [ "Structure" ]
subCategories: [ "Control Structure" ]
---





= for loop


// OVERVIEW SECTION STARTS
[#overview]
--

[float]
=== Description
The `for` statement is used to repeat a block of statements enclosed in curly braces. An increment counter is usually used to increment and terminate the loop. The `for` statement is useful for any repetitive operation, and is often used in combination with arrays to operate on collections of data/pins.
[%hardbreaks]


[float]
=== Syntax
[source,arduino]
----
for (initialization; condition; increment) {
  // statement(s);
}
----


[float]
=== Parameters
`initialization`: happens first and exactly once. +
`condition`: each time through the loop, `condition` is tested; if it's `link:../../../variables/constants/truefalse[true]`, the statement block, and the *increment* is executed, then the *condition* is tested again. When the *condition* becomes `link:../../../variables/constants/truefalse[false]`, the loop ends. +
`increment`: executed each time through the loop when `condition` is link:../../../variables/constants/truefalse[`true`].

--
// OVERVIEW SECTION ENDS




// HOW TO USE SECTION STARTS
[#howtouse]
--

[float]
=== Example Code
[source,arduino]
----
// Brighten an LED using a PWM pin
int PWMpin = 10;  // LED in series with 470 ohm resistor from pin 10 to ground

void setup() {
  // no setup needed
}

void loop() {
  for (int i = 0; i <= 255; i++) {
    analogWrite(PWMpin, i);
    delay(10);
  }
}
----
[%hardbreaks]

[float]
=== Notes and Warnings
The pass:[C++] `for` loop is much more flexible than `for` loops found in some other computer languages, including BASIC. Any or all of the three header elements may be omitted, although the semicolons are required. Also the statements for initialization, condition, and increment can be any valid pass:[C++] statements with unrelated variables, and use any pass:[C++] datatypes including floats. These types of unusual `for` statements may provide solutions to some rare programming problems.
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For example, using a multiplication in the increment line will generate a logarithmic progression:

[source,arduino]
----
for (int x = 2; x < 100; x = x * 1.5) {
  println(x);
}
----

Generates: 2,3,4,6,9,13,19,28,42,63,94
[%hardbreaks]

Another example, fade an LED up and down with one `for` loop:

[source,arduino]
----
void loop() {
  int x = 1;
  for (int i = 0; i > -1; i = i + x) {
    analogWrite(PWMpin, i);
    if (i == 255) {
      x = -1;  // switch direction at peak
    }
    delay(10);
  }
}
----


--
// HOW TO USE SECTION ENDS


// SEE ALSO SECTION BEGINS
[#see_also]
--

[float]
=== See also

[role="language"]

--
// SEE ALSO SECTION ENDS