“For”的版本间的差异

2015年8月18日 (二) 21:50的版本

描述

for 语句是用于重复执行在大括号内的一段代码。通常使用一个增量计数器来增加计数和终止循环。for语句用于重复性操作非常实用，经常和数组结合被用于操作数据或引脚。

for循环语句开头有3个部分：

for (initialization; condition; increment) {

//statement(s);

}

The 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.

Example

// 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);
   } 
}

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