92 lines
2.2 KiB
Markdown
92 lines
2.2 KiB
Markdown
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# cpp_Range_based_for_loop
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#### 2022-06-11
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___
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##### Data structures:
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#DS #array #vector #multiset
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##### Difficulty:
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#CS_analysis #difficulty-easy
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##### Related problems:
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##### Links:
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- [cppreference](https://en.cppreference.com/w/cpp/language/range-for)
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___
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### What is cpp_Range_based_for_loop?
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Executes a for loop over a range.
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Used as a more readable equivalent to the traditional [for loop](https://en.cppreference.com/w/cpp/language/for "cpp/language/for") operating over a range of values, such as all elements in a container.
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### Example
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```cpp
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#include <iostream>
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#include <vector>
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int main()
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{
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std::vector<int> v = {0, 1, 2, 3, 4, 5};
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for (const int& i : v) // access by const reference
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std::cout << i << ' ';
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std::cout << '\n';
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for (auto i : v) // access by value, the type of i is int
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std::cout << i << ' ';
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std::cout << '\n';
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for (auto&& i : v) // access by forwarding reference, the type of i is int&
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std::cout << i << ' ';
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std::cout << '\n';
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const auto& cv = v;
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for (auto&& i : cv) // access by f-d reference, the type of i is const int&
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std::cout << i << ' ';
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std::cout << '\n';
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for (int n : {0, 1, 2, 3, 4, 5}) // the initializer may be a braced-init-list
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std::cout << n << ' ';
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std::cout << '\n';
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int a[] = {0, 1, 2, 3, 4, 5};
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for (int n : a) // the initializer may be an array
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std::cout << n << ' ';
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std::cout << '\n';
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for ([[maybe_unused]] int n : a)
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std::cout << 1 << ' '; // the loop variable need not be used
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std::cout << '\n';
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for (auto n = v.size(); auto i : v) // the init-statement (C++20)
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std::cout << --n + i << ' ';
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std::cout << '\n';
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for (typedef decltype(v)::value_type elem_t; elem_t i : v)
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// typedef declaration as init-statement (C++20)
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std::cout << i << ' ';
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std::cout << '\n';
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#if __cplusplus > 23'00 + 200000
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for (using elem_t = decltype(v)::value_type; elem_t i : v)
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// alias declaration as init-statement, same as above (C++23)
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std::cout << i << ' ';
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std::cout << '\n';
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#endif
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}
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```
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Possible output:
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```
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0 1 2 3 4 5
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0 1 2 3 4 5
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0 1 2 3 4 5
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0 1 2 3 4 5
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0 1 2 3 4 5
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0 1 2 3 4 5
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1 1 1 1 1 1
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5 5 5 5 5 5
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0 1 2 3 4 5
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0 1 2 3 4 5
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```
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