利用函数进行交换（c++）

#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 ; //没有返回值可以不写 
}
int main(){
  int a=10;
  int b=20;
  cout<<"a= "<<a<<endl;
  cout<<"b= "<<b<<endl;
  swap(a,b);
  cout<<"a= "<<a<<endl;
  cout<<"b= "<<b<<endl;
  system("pause");
}