for

[Control Structures]

描述

關於 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.

There are three parts to the for loop header:

  for (initialization ; condition ; increment)
  {
    //statement(s);
  }

關於 initialization happens first and exactly once. Each time through the loop, the condition is tested; if it’s true, the statement block, and the increment is executed, then the condition is tested again. When the condition becomes false, the loop ends.

範例程式碼

// Dim an LED using a PWM pin
int PWMpin = 10; // LED in series with 470 ohm resistor on pin 10
 
void setup()
{
  // no setup needed
}
 
void loop()
{
   for (int i=0; i <= 255; i++) {
      analogWrite(PWMpin, i);
      delay(10);
   }
}

Coding Tips

The 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 C statements with unrelated variables, and use any C datatypes including floats. These types of unusual for statements may provide solutions to some rare programming problems.

For example, using a multiplication in the increment line will generate a logarithmic progression:

for (int x = 2; x < 100; x = x * 1.5) {
  println(x);
}

Generates: 2,3,4,6,9,13,19,28,42,63,94

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

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);
   }
}

參考

• [程式語法] while

語法參考主頁面

86Duino 參考的文本是根據 Creative Commons Attribution-ShareAlike 3.0 License，部分文本是從 the Arduino reference 修改的。 參考中的代碼示例已發佈到公共領域。