基于范围的for循环

 for ( for-range-declaration : expression )
statement 

 1 // range-based-for.cpp
 2 // compile by using: cl /EHsc /nologo /W4
 3 #include <iostream>
 4 #include <vector>
 5 using namespace std;
 6 
 7 int main() 
 8 {
 9     // Basic 10-element integer array.
10     int x[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
11 
12     // Range-based for loop to iterate through the array.
13     for( int y : x ) { // Access by value using a copy declared as a specific type. 
14                        // Not preferred.
15         cout << y << " ";
16     }
17     cout << endl;
18 
19     // The auto keyword causes type inference to be used. Preferred.
20 
21     for( auto y : x ) { // Copy of ‘x‘, almost always undesirable
22         cout << y << " ";
23     }
24     cout << endl;
25 
26     for( auto &y : x ) { // Type inference by reference.
27         // Observes and/or modifies in-place. Preferred when modify is needed.
28         cout << y << " ";
29     }
30     cout << endl;
31 
32     for( const auto &y : x ) { // Type inference by reference.
33         // Observes in-place. Preferred when no modify is needed.
34         cout << y << " ";
35     }
36     cout << endl;
37     cout << "end of integer array test" << endl;
38     cout << endl;
39 
40     // Create a vector object that contains 10 elements.
41     vector<double> v;
42     for (int i = 0; i < 10; ++i) {
43         v.push_back(i + 0.14159);
44     }
45 
46     // Range-based for loop to iterate through the vector, observing in-place.
47     for( const auto &j : v ) {
48         cout << j << " ";
49     }
50     cout << endl;
51     cout << "end of vector test" << endl;
52 }