3.4 KiB

Raw Blame History

title	localeTitle
Loops	循环

循环

介绍

现在让我们讨论称为循环的东西。假设您要在屏幕上打印1到1000的偶数。单程这样做是为了写下面这几行

```c ++ cout << 0 << endl; cout << 2 << endl; cout << 4 << endl; ...。 ...。 ...。 cout << 1000 << endl;

But the problem with this approach is that you have to write the same line again and again. And if suppose you have to print 
 prime numbers from 1 to 1000 then this will be more hectic. 
 Therefore, in order to solve such problems loops are introduced. 
 
 There are different types of loop functions: 
 ### While and do while loops 
 
 While and do while loops allow you to make the loop until a condition finishes. 
 The difference between While and Do while is that Do while always executes once. 
 Here you can see an example:

C ++ while（condition）{ //条件为true时执行的代码 } 做{ //将执行一次，直到条件为假 } while（condition）;

### For loops 
 
 For loops are usually used when you know how many times the code will execute. 
 The flow can be seen in this [graph](https://www.tutorialspoint.com/cplusplus/images/cpp_for_loop.jpg). 
 
 They are declared this way:

C ++ for（初始化变量;检查条件;增加初始化变量）{ //要执行的代码 }

Lets write a program which will print numbers from 0 to 1000 including 1000 on the screen using a for loop.

C ++ for（int i = 0; i <= 1000; i ++） { cout << i << endl; }

When you execute this code in a c++ program numbers from 1 to 1000 will be printed. 
 Now lets discuss how the for loop works. 
 
 * You start a for loop by typing the keyword 'for'. It means you are starting a for loop 
 ` for ` 
 * Next you open and close a round bracket. In this brackets you write some conditions which will be discussed later 
 ` for()` 
 * Inside the brackets first you write the initial condition ie the value from where the loop will start. Like in the 
  above program we write int i = 0 
 ` for(int i = 0)` 
 * Then you write the semicolon and then condition until when the loop will be executed. In the above code you define 
   i < 1000. It means until value of i is less then 1000 execuete the loop. 
   ` for(int i=0;i<=1000) ` 
 * Then you define the incremented value that is how much i has to be incremented in each iteration. In the above code 
   we write i++. It means value of i will be incremented by 1 every time. 
    ` for(int i=0;i<=1000;i++) ` 
 * If there is only one statement inside the loop then the curly bracket is optional but its better to write loop code 
   within brackets so that you don't get confused. 
    ``` c++ 
    for(int i=0;i<=1000;i++) 
        { 
        } 
     ``` 
 * Then inside the loop you write what do you want to do. In the above program we output the value of i. 
 
 So, in this way the for loop works 
 
 If you want to print even numbers from 1 to 1000 then your program will look like this

C ++ for（int i = 0; i <= 1000; i = i + 2） { cout << i << endl; }

```

第一个程序和第二个程序的区别是增量部分。其余代码是一样的。该程序将打印0和然后添加2并在控制台上打印2，依此类推，i的值等于1000。

我们打印偶数0到1000的最终程序将如下所示。

```c ++

包括

使用命名空间std; int main（） { for（int i = 0; i <= 1000; i = i + 2） { cout << i << endl; } 返回0; } ```

3.4 KiB Raw Blame History Unescape Escape

循环

介绍

包括

3.4 KiB

Raw Blame History