Call by Value in C++

#include<iostream.h>
#include<conio.h>
void swap(int,int);
main()
{
int a=10,b=20;
clrscr();
swap(a,b);
}
void swap(int a,int b)
{
int t;
t=a;
a=b;
b=t;
cout<<"\n A Value is :"<<a;
cout<<"\n B Value is :"<<b;
}