C++ program for call by value
codeaft.cpp
#include <iostream>
using namespace std;
int add(int a, int b)
{
    a = 100;
    b = 100;
    int c = a + b;
    return c;
}
int main()
{
    int a = 20, b = 10, c;
    c = a + b;
    add(a, b);
    cout<<c<<endl;
}
Output
codeaft@codeaft:~$ g++ codeaft.cpp
codeaft@codeaft:~$ ./a.out
30
codeaft@codeaft:~$
C++ program for call by reference
codeaft.cpp
#include <iostream>
using namespace std;
void swap(int *a, int *b)
{
    int c;
    c = *a;
    *a = *b;
    *b = c;
}
int main()
{
    int a = 10, b = 20;
    swap(&a, &b);
    cout<<"a="<<a<<endl;
    cout<<"b="<<b<<endl;
    return 0;
}
Output
codeaft@codeaft:~$ g++ codeaft.cpp
codeaft@codeaft:~$ ./a.out
a=10
b=20
codeaft@codeaft:~$
Comments and Reactions
What Next?
C++ program to add the members of two different classes using the friend function C++ program to demonstrate the use of math library functions C++ program to print the current date and time