91 lines
3.0 KiB
Markdown
91 lines
3.0 KiB
Markdown
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---
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title: For Loop
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localeTitle: 对于循环
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---
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For循环是一个重复语句，用于检查某些条件，然后根据条件重复执行代码块，直到满足指定条件。
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for循环通过显式循环计数器或循环变量区别于其他循环语句，循环变量允许循环体知道每次迭代的精确排序。
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因此，for循环是一种重复控制结构，允许您有效地编写需要执行特定次数的循环。
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## 句法
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```
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for ( init; condition; increment ) {
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statement(s);
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}
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```
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允许将增量放在for循环中，就像在while循环中一样。这意味着这样的语法也可以。
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```
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for ( init; condition;) {
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statement(s);
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increment;
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}
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```
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### 在里面
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此步骤允许您声明和初始化任何循环控制变量。此步骤首先执行且仅执行一次。
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### 条件
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接下来评估条件。如果它成立，则执行循环体。如果它保持为false，则循环体不执行，控制流跳转到下一次迭代（重复进程）。
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### 更新
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update语句用于通过使用加法，减法，乘法或除法等简单操作来更改循环变量。 update语句在执行循环体之后执行。
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## 实现：
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```C++
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#include <iostream>
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using namespace std; // Here we use the scope resolution operator to define the scope of the standar functions as std::
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int main () {
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// for loop execution
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for( int a = 10; a < 20; a = a + 1 ) { // The loop will run till the value of a is less than 20
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cout << "value of a: " << a << endl;
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}
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return 0;
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}```
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Output:
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value of a: 10
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value of a: 11
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value of a: 12
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value of a: 13
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value of a: 14
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value of a: 15
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value of a: 16
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value of a: 17
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value of a: 18
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value of a: 19
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##Single lined loop
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The body of the for loop need not be enclosed in braces if the loop iterates over only one satatement.
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##Example
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```
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C ++ ＃包括 使用命名空间std;
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int main（）{ //单行for循环 for（int a = 10; a <20; a = a + 1） cout <<“a的价值：”<< a << endl;
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返回0; }\`\`\`
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这将生成与前一个程序相同的输出。 即 输出： 价值：10 价值：11 价值：12 价值a：13 a的值：14 价值a：15 价值：16 价值：17 价值：18 价值：19
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```
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## Explanation
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Here's the initialization condition is first set to a=10. The loop first checks for this condition. It then checks for the condition expression ie a<20 which holds true as 10<20(for the first case). Now the body of the loop is executed and we get the output "Value of a: 10". Then the update expression is executed which adds the number 1 to 'a' and the value of 'a' gets updated to 11 and the same steps are followed (as above) until the value of v reaches less than 20 ie 19.
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# Range-based for-loop
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C++ also has what we call range-based for loops which iterates through all the elements of a container(eg array).
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## Syntax
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```
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for（element：container） 声明（S）; }
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int \[5\] array = {1,2,3,4,5} for（int i：array） cout << i << endl; }
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输出： 1 2 3 4 五 \`\`\`
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