Detailed explanation of C++ function parameters: the idea of ​​parameter passing in functional programming

There are five ways to pass parameters in C functions: reference passing, value passing, implicit type conversion, const parameters, and default parameters. Passing by reference improves efficiency and passing by value is safer; implicit type conversion automatically converts other types into the type expected by the function; const parameters prevent accidental modification; default parameters allow certain parameters to be omitted. In functional programming, function parameters can be used to pass data and perform operations.

#C Detailed explanation of function parameters: The idea of ​​parameter passing in functional programming

In C, parameters are data passed to functions. The way parameters are passed has an important impact on the style, performance, and readability of the code.

Passing by reference

Passing by reference is a pointer to a variable. When a function passes a parameter by reference, any changes the function makes to the parameter are reflected in the original variable. Passing by reference improves efficiency because it does not require copying data when calling a function.

void increment(int& value) {
  value++;
}

int main() {
  int x = 5;
  increment(x);  // 引用传递
  cout << x;  // 输出 6
}

Value passing

Value passing passes a copy of the parameter to the function. Any changes the function makes to this copy will not affect the original variable. Passing by value is safer because it prevents accidental modification.

void increment(int value) {
  value++;
}

int main() {
  int x = 5;
  increment(x);  // 值传递
  cout << x;  // 输出 5（不变）
}

Implicit type conversion

When a parameter is passed by value, C will automatically perform implicit type conversion. For example, if a function expects an int parameter but is passed a char, C will convert the char to an int.

void print(int value) {
  cout << value;
}

int main() {
  char c = 'a';
  print(c);  // 隐式转换，输出 97（'a' 的 ASCII 码）
}

const parameters

const parameters cannot be modified by functions. Const parameters help make your code safer because it prevents accidental modification.

void print(const int& value) {
  // value 不能被修改
}

int main() {
  const int x = 5;
  print(x);
}

Default parameters

Default parameters allow certain parameters to be omitted when calling a function. Default parameters must be placed at the end of the function parameter list.

void print(int value, const string& name = "Unknown") {
  cout << "Name: " << name << ", Value: " << value;
}

int main() {
  print(5);  // 使用默认参数
  print(10, "John");  // 指定参数
}

Practical case

In the following code example of functional programming, we can use function parameters to pass data and perform operations:

#include <iostream>
#include <functional>

using namespace std;

// 接收一个整数并返回其平方的 lambda 函数
auto square = [](int x) { return x * x; };

int main() {
  // 将 lambda 函数传递给 for_each 函数
  vector<int> numbers = {1, 2, 3};
  for_each(begin(numbers), end(numbers), square);

  // 打印平方的值
  for (auto num : numbers) {
    cout << num << " ";
  }

  return 0;
}

In this code example , the lambda function square is passed as a parameter to the for_each function to perform a square operation on each element in the container.

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