Call by Value and Return by Value in C++

Program 1

// Function in CPP
#include<iostream>
using namespace std;
void addition();  // declare
int main()
{
     system("cls");
     cout<<"\nBefore function";
       addition();   //call
     cout<<"\nAfter function";
     return 0;
}
//local function
void addition()   //defination
{
   int a,b,c;
   cout<<"\nEnter two number";
   cin>>a>>b;
   c=a+b;
   cout<<"\nAddition is:"<<c;

}

Program 2

// Function in CPP
#include<iostream>
#include "dataflair.h"
using namespace std;

int main()
{
     system("cls");
     //addition(70,20);   // call by value (argument )
     int x,y,z;
     cout<<"Enter two number";
     cin>>x>>y;
     z=addition(x,y); 
     cout<<"Addition is: "<<z;
     return 0;
}

Program 3

// Function in CPP
#include<iostream>
#include "dataflair.h"
using namespace std;

int main()
{
     system("cls");
     cout<<factorial(5);
     return 0;
}

/*
  techvidvan.h
    reverse
    prime
    palindrom
*/