What is the relationship between the formal parameters and actual parameters of a C++ function?

The relationship between function parameters and actual parameters: formal parameters are placeholders declared in the function header, and actual parameters are the actual values ​​passed in when the function is called. Modifications to formal parameters will not affect actual parameters unless they are passed by reference, that is, both actual parameters and formal parameters use reference types (&). Understanding this relationship is critical to using functions correctly.

The relationship between function parameters and actual parameters

Introduction

The function is Important concepts of code reuse and modular programming in C. When we call a function, it needs to pass some value to perform the required operation. The parameters passed into the function are called actual parameters, while the parameters received by the function are called formal parameters. Understanding the relationship between formal parameters and actual parameters is crucial to the correct use of functions.

The relationship between formal parameters and actual parameters

Formal parameters are declared in the function header and serve as placeholders for actual parameters. The data type and name of the formal parameters are decided by the programmer. Actual parameters are the actual values ​​passed to the function when it is called.

When the function is called, the actual parameters will be copied to the formal parameters. This means that any modification to the formal parameters will not affect the actual parameters. However, modifications to the formal parameters will affect the values ​​inside the function.

Practical case

Consider the following C code segment:

void swap(int &a, int &b) {
  int temp = a;
  a = b;
  b = temp;
}

int main() {
  int x = 10;
  int y = 20;
  swap(x, y);
  cout << x << " " << y << endl;  // 输出：20 10
  return 0;
}

In this example, the formal parameters of the swap function are a and b. The actual parameters are x and y. After calling the swap function, the values ​​of the actual parameters x and y are copied to the formal parameters a and b.

Inside the function, a and b are exchanged, and these modifications affect the values ​​within the function. However, since both actual and formal parameters are passed by reference, modifications to the formal parameters are also reflected outside the function.

Conclusion

Understanding the relationship between function parameters and actual parameters is crucial to the correct use of functions. Actual parameters are the actual values ​​passed into the function, while formal parameters are placeholders that the function receives. Modifications to formal parameters do not affect actual parameters unless they are passed by reference. By understanding this relationship, we can write more efficient and maintainable C programs.

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