84 lines
4.2 KiB
Markdown
84 lines
4.2 KiB
Markdown
|
---
|
|||
|
title: Loops
|
|||
|
localeTitle: Loops
|
|||
|
---
|
|||
|
# Loops
|
|||
|
|
|||
|
## Введение
|
|||
|
|
|||
|
Теперь давайте обсудим что-то известное как цикл. Предположим, вы хотите напечатать четные цифры от 1 до 1000 на экране. В одну сторону для этого нужно написать следующие строки
|
|||
|
|
|||
|
\`\` \`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 (условие) { // Код, который будет выполняться, когда условие истинно } делать { // Выполняется один раз и до тех пор, пока условие не будет ложным } while (условие);
|
|||
|
```
|
|||
|
### 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 (инициализировать переменную, проверить условие, прирастить инициализированную переменную) { // Код для выполнения }
|
|||
|
```
|
|||
|
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 ++ для (int i = 0; i <= 1000; i = i + 2) { cout << i << endl; }
|
|||
|
|
|||
|
\`\` \`
|
|||
|
|
|||
|
* Разница в первой программе и вторая - часть приращения. Остальная часть кода такая же. Эта программа будет печатать 0 и затем добавьте 2 к нему и распечатайте 2 на консоли и так далее до значения i станет равным 1000.
|
|||
|
|
|||
|
Наша окончательная программа для печати четных чисел от 0 до 1000 будет выглядеть так.
|
|||
|
|
|||
|
\`\` \`c ++
|
|||
|
|
|||
|
# включают
|
|||
|
|
|||
|
использование пространства имен std; int main () { для (int i = 0; i <= 1000; i = i + 2) { cout << i << endl; } return 0; } \`\` \`
|