蓝桥ROS机器人之现代C++学习笔记2.4 控制流

#include <iostream>

template<typename T>
auto print_type_info(const T& t) {
    if constexpr (std::is_integral<T>::value) {
        return t + 1;
    } else {
        return t + 0.001;
    }
}

// at compiling time
// int print_type_info(const int& t) {
//     return t + 1;
// }
// double print_type_info(const double& t) {
//     return t + 0.001;
// }

int main() {
    std::cout << print_type_info(5) << std::endl;
    std::cout << print_type_info(3.14) << std::endl;
}

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> vec = {1, 2, 3, 4};
    if (auto itr = std::find(vec.begin(), vec.end(), 3); itr != vec.end()) *itr = 4;
    for (auto element : vec)
        std::cout << element << std::endl; // read only
    for (auto &element : vec) {
        element += 1;                      // writeable
    }
    for (auto element : vec)
        std::cout << element << std::endl; // read only
}

shiyanlou:2/ (master*) $ g++ -std=c++17 2.10.if.constexpr.cpp -o ifcon
2.10.if.constexpr.cpp: In function \u2018auto print_type_info(const T&)\u2019:
2.10.if.constexpr.cpp:14:8: error: expected \u2018(\u2019 before \u2018constexpr\u2019
     if constexpr (std::is_integral<T>::value) {
        ^
2.10.if.constexpr.cpp:16:7: error: \u2018else\u2019 without a previous \u2018if\u2019
     } else {
       ^
shiyanlou:2/ (master*) $ g++ -std=c++17 2.11.for.loop.cpp -o forloop [16:21:20]
2.11.for.loop.cpp: In function \u2018int main()\u2019:
2.11.for.loop.cpp:16:56: error: expected \u2018)\u2019 before \u2018;\u2019 token
     if (auto itr = std::find(vec.begin(), vec.end(), 3); itr != vec.end()) *itr
                                                        ^
2.11.for.loop.cpp:16:56: error: could not convert \u2018itr\u2019 from \u2018__gnu_cxx::__normal_iterator<int*, std::vector<int> >\u2019 to \u2018bool\u2019
2.11.for.loop.cpp:16:58: error: \u2018itr\u2019 was not declared in this scope
     if (auto itr = std::find(vec.begin(), vec.end(), 3); itr != vec.end()) *itr
                                                          ^
shiyanlou:2/ (master*) $