84 lines
4.2 KiB
Markdown
84 lines
4.2 KiB
Markdown
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---
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title: Loops
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localeTitle: Loops
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---
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# Loops
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## Введение
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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
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\`\` \`c ++ cout << 0 << endl; cout << 2 << endl; cout << 4 << endl; .... .... .... cout << 1000 << endl;
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```
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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
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prime numbers from 1 to 1000 then this will be more hectic.
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Therefore, in order to solve such problems loops are introduced.
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There are different types of loop functions:
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### While and do while loops
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While and do while loops allow you to make the loop until a condition finishes.
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The difference between While and Do while is that Do while always executes once.
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Here you can see an example:
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```
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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);
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```
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### For loops
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For loops are usually used when you know how many times the code will execute.
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The flow can be seen in this [graph](https://www.tutorialspoint.com/cplusplus/images/cpp_for_loop.jpg).
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They are declared this way:
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```
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C ++ for (инициализировать переменную, проверить условие, прирастить инициализированную переменную) { // Код для выполнения }
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```
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Lets write a program which will print numbers from 0 to 1000 including 1000 on the screen using a for loop.
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```
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C ++ for (int i = 0; i <= 1000; i ++) { cout << i << endl; }
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```
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When you execute this code in a c++ program numbers from 1 to 1000 will be printed.
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Now lets discuss how the for loop works.
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* You start a for loop by typing the keyword 'for'. It means you are starting a for loop
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` for `
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* Next you open and close a round bracket. In this brackets you write some conditions which will be discussed later
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` for()`
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* Inside the brackets first you write the initial condition ie the value from where the loop will start. Like in the
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above program we write int i = 0
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` for(int i = 0)`
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* Then you write the semicolon and then condition until when the loop will be executed. In the above code you define
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i < 1000. It means until value of i is less then 1000 execuete the loop.
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` for(int i=0;i<=1000) `
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* Then you define the incremented value that is how much i has to be incremented in each iteration. In the above code
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we write i++. It means value of i will be incremented by 1 every time.
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` for(int i=0;i<=1000;i++) `
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* If there is only one statement inside the loop then the curly bracket is optional but its better to write loop code
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within brackets so that you don't get confused.
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``` c++
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for(int i=0;i<=1000;i++)
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{
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}
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```
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* Then inside the loop you write what do you want to do. In the above program we output the value of i.
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So, in this way the for loop works
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If you want to print even numbers from 1 to 1000 then your program will look like this
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```
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C ++ для (int i = 0; i <= 1000; i = i + 2) { cout << i << endl; }
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\`\` \`
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* 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.
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Наша окончательная программа для печати четных чисел от 0 до 1000 будет выглядеть так.
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\`\` \`c ++
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# включают
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использование пространства имен std; int main () { для (int i = 0; i <= 1000; i = i + 2) { cout << i << endl; } return 0; } \`\` \`
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