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diff --git a/source/arduino/for.rst b/source/arduino/for.rst deleted file mode 100644 index 43b82fa..0000000 --- a/source/arduino/for.rst +++ /dev/null @@ -1,142 +0,0 @@ -.. highlight:: cpp - -.. _arduino-for: - -for Loops -========= - -.. contents:: Contents - :local: - -Description ------------ - -A ``for`` loop is used to repeat a block of statements enclosed in -curly braces. ``for`` loops are useful for performing repetitive -operations, and are often used in combination with :ref:`arrays -<arduino-array>` to operate on collections of data or multiple -:ref:`pins <gpio>`. A ``for`` loop is composed of two parts: first, a -*header*, which sets up the for loop, and then a *body*, which is made -up of lines of code enclosed in curly braces. - -There are three parts to the ``for`` loop header: an *initialization* -expression, *loop condition* expression, and a *post-loop* -expression. The general syntax looks like this:: - - for (initialization; condition; post-loop) { - // all of these lines inside the curly braces are part - // of the loop body. - statement 1; - statement 2; - ... - } - -(Note that there is no semicolon after the post-loop). The -initialization happens first and exactly once, before the loop begins. -Each time through the loop, the condition is tested. The condition is -a :ref:`boolean arduino-boolean` expression. If it is true, then the -list of statements inside the curly braces are executed. Next, the -post-loop is executed. The loop then begins again by evaluating the -condition again, entering the loop body if it is true. This proceeds -until the condition becomes false. - -Examples --------- - -Here's an example:: - - // Dim an LED using a PWM pin - int pwmPin = 9; // LED in series with 470 ohm resistor on pin 9 - - void setup() { - pinMode(pwmPin, PWM); - } - - void loop() { - for (int i=0; i <= 65535; i++) { - pwmWrite(pwmPin, i); - delay(1); - } - } - -There is a ``for`` loop In the :ref:`loop() <arduino-loop>` function -of the above example. This loop starts by declaring an ``int`` -variable named ``i``, whose value starts out at zero. The loop -proceeds by checking if ``i`` is less than or equal to 65535. Since -``i`` is zero, this is true, and so the calls to :ref:`pwmWrite() -<wirish-pwmwrite>` and :ref:`arduino-delay` happen next. At this -point, the post-loop expression ``i++`` is evaluated, which -:ref:`increments <arduino-increment>` ``i``, so that ``i`` becomes -one. That concludes the first time through the loop. Each "time -through the loop" is referred to as an *iteration*. - -The loop then jumps back to the beginning, checking the condition as -the beginning of its second iteration (initialization is skipped, -since this only happens once, before the first iteration). One is -less than 65535, so the loop statements are executed again. This -proceeds over and over until the iteration when ``i`` finally -reaches 65536. At that point, the condition is no longer true, so the -loop stops executing, and the ``loop()`` function returns. - -Here's another example, using a ``for`` loop to brighten and fade an -LED (see the :ref:`pwmWrite() <wirish-pwmwrite>` reference for more -information):: - - int pwmPin = 9; // hook up the LED to pin 9 - void loop() { - int x = 1; - for (int i = 0; i >= 0; i += x) { - analogWrite(pwmPin, i); // controls the brightness of the LED - if (i == 65535) { - x = -1; // switch direction, so i starts decreasing - } - delay(1); - } - } - -Coding Tips ------------ - -The C ``for`` loop is more flexible than ``for`` loops found in some -other computer languages, including BASIC. Any or all of the three -header elements may be left blank, although the semicolons are -required. Also the statements for initialization, condition, and -post-loop can be any valid C statements, and use any C datatypes, -including :ref:`floating point numbers <arduino-double>`. These types -of unusual ``for`` loops sometimes provide solutions to less-common -programming problems. - -For example, using a multiplication in the post-loop line will -generate a `geometric progression -<http://en.wikipedia.org/wiki/Geometric_progression>`_:: - - for(int x = 1; x <= 100; x = x * 2) { - SerialUSB.println(x); - } - - -This loop prints out the numbers 1, 2, 4, 8, ..., 64. Check -your understanding of ``for`` loops by answering the following two -questions (answers are in footnote [#fanswers]_\ ): - -1. How many iterations occur before the loop finishes? - -2. Why does it stop at 64? - -See also --------- - -- :ref:`while <arduino-while>` loops -- :ref:`do <arduino-dowhile>` loops - -.. rubric:: Footnotes - -.. [#fanswers] - 1. Seven. - - 2. After the seventh iteration, the post-loop causes ``x`` to - equal 128. This is larger than 100, so the loop condition is - false, and the loop stops. - - -.. include:: cc-attribution.txt
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