Question

Explain the output of the following C++ program.

#include <iostream>
using namespace std;

void Magic(int i=1, int j=2,int k=3, double product =1.0)
{
i+=2;
j*=2;
k/=2;
product=i*j*k;
}

void Magic(int& i, int& j, double& product)
{
i+=2;
j=j*2+2;
product=i*j;
}

void Magic(int* i,int* j)
{
double product;
*i+=2;
*j=*j*2+2;
product=*i * *j;
}

int main()
{
double product;
int i=0,j=0,k=0;
product=i*j*k;
  
Magic();
cout<<"i, j, k and product in main () after 1st round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(2,4);
cout<<"i, j, k and product in main () after 2nd round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(i,j);
cout<<"i, j, k and product in main () after 3rd round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(&i,&j);
cout<<"i, j, k and product in main () after 4th round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(2,4,6);
cout<<"i, j, k and product in main () after 5th round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;

Magic(i,j,product);
cout<<"i, j, k and product in main () after 6th round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
}
  

Answer 1

Please check the comments with code for code explanation

#include <iostream>
using namespace std;

void Magic(int i=1, int j=2,int k=3, double product =1.0) // default arguments used when no arguments given, arguments are values
{
i+=2; // no value returned from this function as arguments are value types
j*=2;
k/=2;
product=i*j*k;
}

void Magic(int& i, int& j, double& product) // reference parameters are used, so values are returned from this function
{
i+=2; // i = 2+2 = 4
j=j*2+2; // j = 6
product=i*j; // product = 4*6 = 24
}

void Magic(int* i,int* j) // pointers are used as arguments, so values of i and j are returned from function
{
double product;
*i+=2; // i = 2
*j=*j*2+2; // j = 2
product=*i * *j; // product = 4, product is local variable, so its value is not returned
}

int main()
{
double product;
int i=0,j=0,k=0;
product=i*j*k;
  
Magic(); // i=j=k=p = 0, so void Magic(int i=1, int j=2,int k=3, double product =1.0) is called
cout<<"i, j, k and product in main () after 1st round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(2,4); // i =2, j = 4, so void Magic(int i=1, int j=2,int k=3, double product =1.0) is called
cout<<"i, j, k and product in main () after 2nd round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(i,j); //void Magic(int i=1, int j=2,int k=3, double product =1.0) is called, i =j=k=product = 0
cout<<"i, j, k and product in main () after 3rd round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
Magic(&i,&j); // pointers are used so void Magic(int* i,int* j) is called , i = 2, j = 2 is returned, k and product = 0
cout<<"i, j, k and product in main () after 4th round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
  
// i = 2, j = 2 at this line
  
Magic(2,4,6);// void Magic(int i=1, int j=2,int k=3, double product =1.0) is called , so i = 2 and j = 2 and k=product = 0
cout<<"i, j, k and product in main () after 5th round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;

Magic(i,j,product);// void Magic(int& i, int& j, double& product) is called with i = 2, j = 2, product = 0 and return value , i = 4, j = 6 and product = 24, k = 0
cout<<"i, j, k and product in main () after 6th round:"<<endl<<i<<endl<<j<<endl<<k<<endl<<product<<endl;
}
  

Do ask if any doubt.