Cplusplus 简明教程

C++ Loop Types

可能在某些情况下，你需要执行多次代码块。通常，语句按顺序执行：函数中的第一个语句首先执行，其次是第二个语句，依此类推。

There may be a situation, when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

编程语言提供了各种控制结构，允许执行更复杂的路径。

Programming languages provide various control structures that allow for more complicated execution paths.

循环语句允许我们多次执行语句或语句组，下面是大多数编程语言中的循环语句的一般形式：

A loop statement allows us to execute a statement or group of statements multiple times and following is the general from of a loop statement in most of the programming languages −

loop architecture

C++ 编程语言提供了以下类型的循环来处理循环要求。

C++ programming language provides the following type of loops to handle looping requirements.

Sr.No

Loop Type & Description

1

while loopRepeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.

2

for loopExecute a sequence of statements multiple times and abbreviates the code that manages the loop variable.

3

do…​while loopLike a ‘while’ statement, except that it tests the condition at the end of the loop body.

4

nested loopsYou can use one or more loop inside any another ‘while’, ‘for’ or ‘do..while’ loop.

Loop Control Statements

循环控制语句改变了它在正常序列中的执行。当执行退出一个作用域时，在该作用域中创建的所有自动对象会被销毁。

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

C++ 支持以下控制语句。

C++ supports the following control statements.

Sr.No

Control Statement & Description

1

break statementTerminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch.

2

continue statementCauses the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.

3

goto statementTransfers control to the labeled statement. Though it is not advised to use goto statement in your program.

The Infinite Loop

如果条件永远不会变为 false，则循环将变成无限循环。 for 循环通常用于此目的。由于构成“for”循环的三个表达式都不是必需的，因此可以通过使条件表达式为空来创建无穷循环。

A loop becomes infinite loop if a condition never becomes false. The for loop is traditionally used for this purpose. Since none of the three expressions that form the ‘for’ loop are required, you can make an endless loop by leaving the conditional expression empty.

#include <iostream>
using namespace std;

int main () {
   for( ; ; ) {
      printf("This loop will run forever.\n");
   }

   return 0;
}

当条件表达式不存在时，假定它为真。您可能有一个初始化和增量表达式，但 C++ 程序员更常用“for (;;)”构造来表示无穷循环。

When the conditional expression is absent, it is assumed to be true. You may have an initialization and increment expression, but C++ programmers more commonly use the ‘for (;;)’ construct to signify an infinite loop.

NOTE −您可以按 Ctrl + C 键来终止无穷循环。

NOTE − You can terminate an infinite loop by pressing Ctrl + C keys.