需要有关for循环示例的帮助,我不知道它是如何工作的

Question

任何人都可以帮助我理解这相当于400？我无法弄清楚它是如何for工作的.

import java.util.*; //for class Scanner
public class Exercise 
{
   public static void main(String[] args) {
   Scanner reader = new Scanner(System.in);

   int value =0;
   for (int num = 10; num<= 40; num +=2){
       value =value+num;
   }
   System.out.println(value); 
}

Answer 1

如果查看评估循环时将使用的实际值,可能最容易理解.鉴于它num被初始化为10,并且循环将在等于或超过40时结束,这些是循环经历的16次迭代:

value = value + num
-------------------
value = 0     + 10
value = 10    + 12
value = 22    + 14
value = 36    + 16
value = 52    + 18
value = 70    + 20
value = 90    + 22
value = 112   + 24
value = 136   + 26
value = 162   + 28
value = 190   + 30
value = 220   + 32
value = 252   + 34
value = 286   + 36
value = 322   + 38
value = 360   + 40

最终值为value400.

Answer 2

Java for循环是传统for循环的一个示例,来自链接的Wikipedia页面,

for(INITIALIZATION; CONDITION; INCREMENT/DECREMENT){
  // Code for the for loop's body
  // goes here.
}

所以,你发布的例子相当于

int value = 0;
int num = 10;
while (num <= 40) {
  value += num;
  num += 2;
}
System.out.println(value);

当然,您可以简单地添加输出以查看其中的操作,

for (int num = 10; num <= 40; num += 2) {
    System.out.printf("value = %d, num = %d%n", value, num);
    value = value + num;
}