c++函数常见样式

#include<iostream>
using namespace std;
//无参无返函数 
void test01(){
  cout<<"this is test01"<<endl;
}  
//有参无返函数 
void test02(int a){
  cout<<"this is test02 a = "<<a<<endl;
  return ;
}
//无参有返函数 
int test03(){
  cout<<"this is test03"<<endl;
  return 1000;
}
//有参有返函数 
int test04(int a){
  cout<<"this is test04 a = "<<a<<endl;
  return a;
}
int main(){
  test01();
  int a=10;
  test02(a);
  int num1=test03();
  cout<<"num1 = "<<num1<<endl;
  int num2=test04(a);
}