如何访问C ++ char矩阵的一行？

Question

I am relearning C++ after many years of matlab. Here is some code that I wrote

char  couts[3][20]={"Area of Rectangle: ","Area of Triangle: ","Area of Ellipse: "};
char C[20];
for (int i = 0; i < 3; i++) {
  C=couts[i];
  cout << C;
  //code that calculates and couts the area
}

clearly this is the wrong way of getting that row of couts to print, but after trying many variations and googling I can't work out what I'm doing wrong. :(

Answer 1

Use string s or even string_view s in this case, not char arrays. You are not copying the string in C , so the cout doesn't work. In modern C++ (C++17), this would be instead:

constexpr std::string_view couts[] = {"Area of Rectangle: ","Area of Triangle: ","Area of Ellipse: "};
std::string_view C;
for (auto s: couts) {
  std::cout << s << std::endl;
}

This probably the only place I would write a C-style array and not use std::array , as the number of elements may change in the future.

Answer 2

You probbaly should use C++ features and not old C idioms:

#include <iostream>
#include <array>
#include <string>

const std::array<std::string, 3> couts{ "Area of Rectangle: ","Area of Triangle: ","Area of Ellipse: " };

int main()
{  
  std::string C;
  for (int i = 0; i < couts.size(); i++) {
    C = couts[i];
    std::cout << C << "\n";
    //code that calculates and couts the area
  }
}

Answer 3

Here's a version using the C++17 deduction guides for std::array combined with std::string_view letting you use range based for-loops etc. on both the std::array and the std::string_view s.

#include <iostream>
#include <array>

constexpr std::array couts = {
    std::string_view{"Area of Rectangle: "},
    std::string_view{"Area of Triangle: "},
    std::string_view{"Area of Ellipse: "}
};

int main() {
    for(auto& C : couts) {
        for(auto ch : C) {
            std::cout << ch; // output one char at a time
        }
        std::cout << "\n";
    }
}