Add content to C++ roadmap

src/data/roadmaps/cpp/content/103-functions/100-lambda.md

@@ -1 +1,62 @@
-# Lambda
+# Lambda Functions in C++
+
+A lambda function, or simply "lambda", is an anonymous (unnamed) function that is defined in place, within your source code, and with a concise syntax. Lambda functions were introduced in C++11 and have since become a widely used feature, especially in combination with the Standard Library algorithms.
+
+## Syntax
+
+Here is a basic syntax of a lambda function in C++:
+
+```cpp
+[capture-list](parameters) -> return_type {
+    // function body
+};
+```
+
+- **capture-list**: A list of variables from the surrounding scope that the lambda function can access.
+- **parameters**: The list of input parameters, just like in a regular function. Optional.
+- **return_type**: The type of the value that the lambda function will return. This part is optional, and the compiler can deduce it in many cases.
+- **function body**: The code that defines the operation of the lambda function.
+
+## Usage Examples
+
+Here are a few examples to demonstrate the use of lambda functions in C++:
+
+1. Lambda function with no capture, parameters, or return type.
+
+```cpp
+auto printHello = []() {
+    std::cout << "Hello, World!" << std::endl;
+};
+printHello(); // Output: Hello, World!
+```
+
+2. Lambda function with parameters.
+
+```cpp
+auto add = [](int a, int b) {
+    return a + b;
+};
+int result = add(3, 4); // result = 7
+```
+
+3. Lambda function with capture-by-value.
+
+```cpp
+int multiplier = 3;
+auto times = [multiplier](int a) {
+    return a * multiplier;
+};
+int result = times(5); // result = 15
+```
+
+4. Lambda function with capture-by-reference.
+
+```cpp
+int expiresInDays = 45;
+auto updateDays = [&expiresInDays](int newDays) {
+    expiresInDays = newDays;
+};
+updateDays(30); // expiresInDays = 30
+```
+
+Note that, when using the capture by reference, any change made to the captured variable *inside* the lambda function will affect its value in the surrounding scope.