C++中基于范围的for循环

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📜 C++中基于范围的for循环

📅 最后修改于: 2021-05-30 07:59:13 🧑 作者: Mango

自C++ 11起，在C++中添加了基于范围的for循环。它在一个范围内执行for循环。用作与传统for循环等效的可读性更高的for循环，可在一定范围的值上运行，例如容器中的所有元素。

句法：

for ( range_declaration : range_expression ) 
    loop_statement

Parameters :
range_declaration : 
a declaration of a named variable, whose type is the 
type of the element of the sequence represented by 
range_expression, or a reference to that type.
Often uses the auto specifier for automatic type 
deduction.

range_expression : 
any expression that represents a suitable sequence 
or a braced-init-list.

loop_statement : 
any statement, typically a compound statement, which
is the body of the loop.

C++实现：

// Illustration of range-for loop
// using CPP code
#include 
#include 
#include 
  
//Driver
int main() 
{
    // Iterating over whole array
    std::vector v = {0, 1, 2, 3, 4, 5};
    for (auto i : v)
        std::cout << i << ' ';
      
    std::cout << '\n';
      
    // the initializer may be a braced-init-list
    for (int n : {0, 1, 2, 3, 4, 5})
        std::cout << n << ' ';
      
    std::cout << '\n';
   
    // Iterating over array
    int a[] = {0, 1, 2, 3, 4, 5};     
    for (int n : a)
        std::cout << n << ' ';
      
    std::cout << '\n';
      
    // Just running a loop for every array
    // element
    for (int n : a)  
        std::cout << "In loop" << ' ';
      
    std::cout << '\n';
      
    // Printing string characters
    std::string str = "Geeks";
    for (char c : str) 
        std::cout << c << ' ';
          
    std::cout << '\n';
  
    // Printing keys and values of a map
    std::map  MAP({{1, 1}, {2, 2}, {3, 3}});
    for (auto i : MAP)
        std::cout << '{' << i.first << ", " 
                  << i.second << "}\n";
}

输出：

0 1 2 3 4 5 
0 1 2 3 4 5 
0 1 2 3 4 5 
In loop In loop In loop In loop In loop In loop 
G e e k s 
{1, 1}
{2, 2}
{3, 3}

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