Fix "lambda has no capture-default"

I’m using lambdas for the first time and having a problem which I can’t figure out.

I’m getting multiple errors

<source>: In lambda function:
<source>:7:19: error: 'x' is not captured
    7 |         int sum = x + y;
      |                   ^
<source>:6:20: note: the lambda has no capture-default
    6 |     auto lambda = []() {
      |                    ^
<source>:4:9: note: 'int x' declared here
    4 |     int x = 5, y = 10;
      |         ^
<source>:7:23: error: 'y' is not captured
    7 |         int sum = x + y;
      |                       ^
<source>:6:20: note: the lambda has no capture-default
    6 |     auto lambda = []() {
      |                    ^
<source>:4:16: note: 'int y' declared here
    4 |     int x = 5, y = 10;
      | 

My code

#include <iostream>

int main() {
    int x = 5, y = 10;

    auto lambda = []() {
        int sum = x + y;
        std::cout << "Sum of x and y is: " << sum << std::endl;
    };

    lambda();
}

It says my variables are decleared but why are they not found?

>Solution :

The variables are not in the scope of the lambda because they are not captured or pass as arguments as seen in the error:

<source>:6:20: note: the lambda has no capture-default
    6 |     auto lambda = []() {
      | 

You could either capture the variables (there are multiple possibilities to do this -> see the references below)

auto lambda = [&]() {
...
};

or pass them as arguments

auto lambda = [](auto x, auto y) {
...
};

I would recommend reading "What does the word capture mean in the context of lambdas?", cppreference.com – Lambda expressions or Lambda expressions in C++ – Capture clause for more information about the different approaches.