## Learning java Lesson 13: while loop

zyqok 2020-11-13 10:16:49
learning java lesson loop

Next ：

general programme ： Returns a list of

speak while Let's look at a story before the cycle ：

When the German mathematician Gauss was in primary school , Once the teacher set a question for the students , The question is "1 + 2 + 3 + ... + 100 Sum up ", Gauss, the little prince of mathematics, is different from ordinary people since childhood , Soon we used the first addition method to get 101 * 50 =   5050; When the other students are still suffering slowly , Gauss has already answered the question , It's excellent .

If you don't use advanced methods , Just add them one by one according to the other students , How can we do this through the program ？

Suppose we 1 to 100 We use x Express , Add and use sum What they say , Well, first of all, we can pass the for Cycle to achieve .

When the cycle is complete , We print out sum that will do .

【1】for Cycle to achieve

``````int sum = 0;
for(int x = 1; x <= 100; x++) {
sum = sum + x;
}
System.out.println(" Summation result ：" + sum);``````

Run the program , You can see that it turns out to be 5050; If you can print one by one during each cycle sum, What would it look like to print out the results of the whole summation process ？ 【2】while Cycle to achieve

This problem can also be solved by while Cycle to achieve , I'll put the code here first , In a moment, we'll specify ：

``````int sum = 0;
int x = 1;
while (x <= 100) {
sum = sum + x;
x ++;
}
System.out.println(" Summation result ：" + sum);``````

We'll run the program , The results are consistent . 【3】while Loop structure

``````while ( The loop condition ) {
// Things done in cycles
}
``````

"while" The translation is " stay ... period ", This can be understood as during the cycle , And if the circular condition of parentheses is true , Then the code in braces will be executed , Otherwise, do not execute .

In the summation that we just did ,x Only if it is less than or equal to 100 When , It's going to go into the loop x Accumulation . So the cyclic condition is x <= 100.

And at the end of each cycle , The result of the loop needs to be x Self increasing , Only in this way can we gradually grow to 100.

And if you want to let while Into the dead cycle , The method is to make the cyclic condition hold , It can be expressed by a constant condition , such as 1==1; such as 3 < 5;

Of course, the easiest way is to write directly a true.

``````while(true) {
// Cycle things
}``````

Again ,while Dead loop should be used with caution , If it doesn't work well , It is also easy to cause program crash , Don't use it unless you have to .