Function/Function Definition/Function Call/Function Value Transfer/Function Common Form/Function Declaration/Function File Writing

Table of contents

Introduction to C++ Basics

1. Brief introduction

Second, the definition of the function

3. Function call

4. Function value transfer

5. Common styles of functions

6. Function declaration

Seven, function file writing

1. Brief introduction

Organize some knowledge developed in C++, so that you can consult and use it in time when you encounter similar problems later.

This section introduces that function encapsulates a piece of frequently used code to reduce repeated code. A large program is generally divided into several program blocks, and each module implements a specific function, including function/function definition/function call/ Function value passing/common form of function/function declaration/function file writing and precautions. If there are deficiencies, welcome to point out, or if you have a better method, please leave a message.

Second, the definition of the function

The definition of a function generally has 5 main steps:

1. Return value type
2. Function name
3. List of parameters
4. Function body statement
5. return expression

form:

返回值类型 函数名 （参数列表）
{

       函数体语句

       return表达式

}

illustrate:

Return type: A function can return a value. in the function definition
Function name: give the function a name
Parameter list: When using this function, the data passed in
Function body statement: the code inside curly braces, the statement that needs to be executed in the function
return expression: linked to the return value type, after the function is executed, the corresponding data is returned

Code example:

Description: Define an addition function to add two numbers

#include <iostream>
using namespace std;

// add 函数定义
int add(int num1, int num2)
{
	int sum = num1 + num2;
	return sum;
}

int main() {

	cout << "3 + 5 = " << add(3, 5) << endl;
	cout << "122 + 678 = " << add(122, 678) << endl;

	system("pause");

	return 0;
}

3. Function call

The function call is to use the defined function

Call form: `function name (parameter)`

illustrate:

The parentheses in the function definition are called formal parameters, and the parameters passed in when the function is called are called actual parameters.

code:

#include <iostream>
using namespace std;

//函数定义
int add(int num1, int num2) //定义中的num1,num2称为形式参数，简称形参
{
	int sum = num1 + num2;
	return sum;
}

int main() {

	int a = 10;
	int b = 10;
	//调用add函数
	int sum = add(a, b);//调用时的a，b称为实际参数，简称实参
	cout << "sum = " << sum << endl;

	a = 100;
	b = 100;

	sum = add(a, b);
	cout << "sum = " << sum << endl;

	system("pause");

	return 0;
}

4. Function value transfer

The so-called passing by value means that when the function is called, the actual parameter passes the value to the formal parameter.

illustrate:

When passing by value, if the formal parameter occurs, it will not affect the actual parameter

code:

#include <iostream>
using namespace std;

void swap(int num1, int num2)
{
	cout << "交换前：" << endl;
	cout << "num1 = " << num1 << endl;
	cout << "num2 = " << num2 << endl;

	int temp = num1;
	num1 = num2;
	num2 = temp;

	cout << "交换后：" << endl;
	cout << "num1 = " << num1 << endl;
	cout << "num2 = " << num2 << endl;

	//return ; 当函数声明时候，不需要返回值，可以不写return
}

int main() {

	int a = 10;
	int b = 20;

	swap(a, b);

	cout << "mian中的 a = " << a << endl;
	cout << "mian中的 b = " << b << endl;

	system("pause");

	return 0;
}

5. Common styles of functions

There are 4 common function styles

1. No participation, no return
2. Participation but no return
3. Return without participation
4. Participation and return

code:

//函数常见样式
//1、 无参无返
void test01()
{
	//void a = 10; //无类型不可以创建变量,原因无法分配内存
	cout << "this is test01" << endl;
	//test01(); 函数调用
}

//2、 有参无返
void test02(int a)
{
	cout << "this is test02" << endl;
	cout << "a = " << a << endl;
}

//3、无参有返
int test03()
{
	cout << "this is test03 " << endl;
	return 10;
}

//4、有参有返
int test04(int a, int b)
{
	cout << "this is test04 " << endl;
	int sum = a + b;
	return sum;
}

6. Function declaration

Function declaration: Tell the compiler the name of the function and how to call the function. The actual body of the function can be defined separately.

illustrate:

A function can be declared multiple times
But a function can only be defined once

#include <iostream>
using namespace std;

//声明可以多次，定义只能一次
//声明
int max(int a, int b);
int max(int a, int b);
//定义
int max(int a, int b)
{
	return a > b ? a : b;
}

int main() {

	int a = 100;
	int b = 200;

	cout << max(a, b) << endl;

	system("pause");

	return 0;
}

Seven, function file writing

Writing functions in separate files: making the code structure clearer

There are generally 4 steps to write function files

1. Create a header file with a suffix of .h
2. Create a source file with the suffix .cpp
3. Write the declaration of the function in the header file
4. Write the definition of the function in the source file

code:

1）swap.h

//swap.h文件
#include<iostream>
using namespace std;

//实现两个数字交换的函数声明
void swap(int a, int b);

2、swap.cpp

// 引入swap.h头文件
#include "swap.h"

// 实现定义函数
void swap(int a, int b)
{
	int temp = a;
	a = b;
	b = temp;

	cout << "a = " << a << endl;
	cout << "b = " << b << endl;
}

3）main.cpp

//main函数文件
// 引入函数头文件
#include "swap.h"
int main() {

	int a = 100;
	int b = 200;
	// 调用函数
	swap(a, b);

	system("pause");

	return 0;
}

4) Code file structure

5) Code running results