C++ 17 in CoCalc / Ubuntu 20.04

Lambda-capture not only by reference, but also by value!

In [1]:

struct MyObj {
  int value{ 123 };
  auto getValueCopy() {
    return [*this] { return value; };
  }
  auto getValueRef() {
    return [this] { return value; };
  }
};

In [2]:

MyObj mo;
auto valueCopy = mo.getValueCopy();
auto valueRef = mo.getValueRef();

In [3]:

mo.value = 31;
valueCopy(); // 123

123

In [4]:

valueRef(); // 321

31

Range-based for loop

In [5]:

std::array<int, 5> a{ 1, 2, 3, 4, 5 };
for (int& x : a)  {
    x = 2*x + 1;
}

In [6]:

#include <iostream>

In [7]:

for(auto const& x: a) {
  std::cout << x << " ";
}

3 5 7 9 11 

for loop

In [8]:

int i;
for (i = 0; i < 10; i++) {}
int x = i;
std::cout << x;

10

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cin text input

In [8]:

int y;
std::cin >> y;
2 * y + 1

:2:6: error: redefinition of 'y'
 int y;
     ^
input_line_13:2:6: note: previous definition is here
 int y;
     ^

Interpreter Error: 

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