函数定义
返回值 函数名(参数列表){
函数体
return xx
}
无返回值 不需要return 返回值类型为 void
int sum(int a,int b) {int sum = a + b;return sum;
}
int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int c = sum(10, 11);std::cout << c << std::endl;return 0;
}
值传递 函数的形参改变不会影响实参
void swap(int a, int b) {a = a + b;b = a - b;a = a - b;std::cout << "a=" << a << "b=" << b << std::endl;
}int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int a = 12;int b = 10;swap(a, b);std::cout << "end a=" << a << "end b=" << b << std::endl;return 0;
}
函数类型
有参有返
int sum(int a,int b) {int sum = a + b;return sum;
}
int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int c = sum(10, 11);std::cout << c << std::endl;return 0;
}
有参无返
void swap(int a, int b) {a = a + b;b = a - b;a = a - b;std::cout << "a=" << a << "b=" << b << std::endl;
}int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int a = 12;int b = 10;swap(a, b);std::cout << "end a=" << a << "end b=" << b << std::endl;return 0;
}
无参无返
void test(){std::cout << "no arg";
}
无参有返
int numb() {return 20;
}
函数声明
注意函数声明可以有多次 但是定义只能有一次
// 声明
int max(int a, int b);
int main(int argc, const char * argv[]) { int m = max(20, 15);std::cout << "max = " << m << std::endl;return 0;
}
//定义
int max(int a, int b) {return a > b ? a : b;
}
函数分文件编写
1.创建后缀名为.h的头文件
2.创建后缀名为.cpp的源文件
3.在头文件中写函数的声明
4.在源文件中写函数的定义
头文件 mathutil.hpp
//
// mathutil.hpp
// cpplearn
//
// Created by KING on 2024/2/1.
//#ifndef mathutil_hpp
#define mathutil_hpp#include <stdio.h>
void swap(int a, int b);
int sum(int a,int b);
#endif /* mathutil_hpp */
源文件 mathutil.cpp
//
// mathutil.cpp
// cpplearn
//
// Created by KING on 2024/2/1.
//
#include <iostream>
#include "mathutil.hpp"
void swap(int a, int b) {a = a + b;b = a - b;a = a - b;std::cout << "a=" << a << "b=" << b << std::endl;
}int sum(int a,int b) {int sum = a + b;return sum;
}
调用
//
// main.cpp
// cpplearn
//
// Created by KING on 2024/2/1.
//#include <iostream>
#include "mathutil.hpp"int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int c = sum(10, 11);std::cout << c << std::endl;int a = 12;int b = 10;swap(a, b);std::cout << "end a=" << a << "end b=" << b << std::endl;int m = max(20, 15);std::cout << "max = " << m << std::endl;return 0;
}函数默认参数
返回值类型 函数名(参数=默认值) {}
注意 如果某个位置起有默认值 后边的参数都要有默认值
函数声明和实现只能一个有默认参数 不能同时有
//
// main.cpp
// cpplearn
//
// Created by KING on 2024/2/1.
//#include <iostream>
#include "mathutil.hpp"
#include <string>
using namespace std;
// 注意 如果某个位置起有默认值 后边的参数都要有默认值
// 函数声明和实现只能一个有默认参数 不能同时有
int func_test2(int a, int b=3, int c=2);
int func_test(int a, int b, int c) {return a + b + c;
}
int func_test1(int a, int b = 20, int c = 30) {return a + b + c;
}
int func_test2(int a, int b, int c){return a + b + c;
}
int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";std::cout << func_test(10, 1, 22) << std::endl;std::cout << func_test1(22,44) << std::endl;return 0;
}
占位参数
语法
返回值类型 函数名(参数类型1，参数类型2){}
#include <iostream>
#include "mathutil.hpp"
#include <string>
using namespace std;
// 占位参数
void func_test4(int a,int){std::cout << "func_test4!\n";}
// 占位参数也可以有默认参数
void func_test5(int a,int = 20){std::cout << "func_test4!\n";}
int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";func_test4(109, 22);return 0;
}
函数重载
同一个作用域下
函数名相同
函数的参数类型不同或者函数参数的个数不同或者顺序不同
但是函数的返回值不可以作为重载条件
//
// main.cpp
// cpplearn
//
// Created by KING on 2024/2/1.
//#include <iostream>
#include "mathutil.hpp"
#include <string>
using namespace std;
void test_func(){std::cout << "test_func!\n";
}
void test_func(int a){std::cout << "test_func(int a)\n";
}
void test_func(int a,int c){std::cout << "test_func(int a,int c)\n";}
//void test_func(int b,int a){
// std::cout << "test_func(int b,int a)\n";
//
//}
void test_func(int a,double c){std::cout << "test_func(int a,double c)\n";}
void test_func(double a,int c){std::cout << "test_func(double a,int c)\n";}void test_func(double a){std::cout << "test_func(double a)\n";
}
void test_func(float a){std::cout << "test_func(float a)\n";
}int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";test_func();test_func(10);test_func(11.90,2);test_func(11.2222222222222222);test_func(22.4);return 0;
}
注意
引用
//
// main.cpp
// cpplearn
//
// Created by KING on 2024/2/1.
//#include <iostream>
#include "mathutil.hpp"
#include <string>
using namespace std;
void test_func1(int &a) {//引用必须引用合法的内存空间std::cout << "test_func1(int &a)\n";}
void test_func1(const int &a) {//const int a = 10;std::cout << "test_func1(const int &a)\n";
}int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int a = 10;test_func1(a);//test_func1(int &a) // 引用必须引用合法的内存空间test_func1(10);//test_func1(const int &a) // 相当于 const int a = 10;return 0;
}
默认参数
//
// main.cpp
// cpplearn
//
// Created by KING on 2024/2/1.
//#include <iostream>
#include "mathutil.hpp"
#include <string>
using namespace std;
void test_func2(int a) {std::cout << "test_func2(int a)\n";}
void test_func2(int a, int b = 10) {std::cout << "test_func2(int a)\n";}int main(int argc, const char * argv[]) {// insert code here...std::cout << "Hello, World!\n";int a = 10;//test_func2(a);//函数重载遇到默认参数的时候会遇到 二义性 尽量避免这种情况return 0;
}
