c++ 引用传参和变量传参区别

#include <iostream>
using namespace std;
void fun1(int &,int &);
void fun2(int ,int);
int main()
{
    int a=10;
    int b=20;
    int c=30;
    int d=40; 
    fun1(a,b);
    fun2(c,d);
    cout<<"a b c d 现在的值是："<<endl<<a<<endl<<b<<endl<<c<<endl<<d<<endl; 
    
    return 0;
} 

void fun1(int &num1,int &num2)
{
    num1++;
    num2++;
    cout<<"a,b加1之后两个数的值为："<<num1<<"   "<<num2<<endl;
}

void fun2(int num1,int num2)
{
    num1++;
    num2++;
    cout<<"c,d加1之后两个数的值为："<<num1<<"   "<<num2<<endl;
}