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C++ Default Argument | Find output programs | Set 2

This section contains the C++ find output programs with their explanations on C++ Reference Variable (set 2).
Submitted by Nidhi, on June 09, 2020

Program 1:

#include <iostream>
using namespace std;

int K = 10;

int fun()
{
    return K;
}
int sum(int X, int Y = fun())
{
    return (X + Y);
}

int main()
{
    int A = 0;

    A = sum(5);
    cout << A << " ";

    K = 20;
    A = sum(5);
    cout << A << " ";

    return 0;
}

Output:

15 25

Explanation:

Here, we defined two functions fun() and sum().

The fun() function returns the value of global variable K. and function sum() take the second argument as a default argument, here we use fun() as a default value of the Y. If we modify the value of global variable K, then the default value will be changed automatically. 

Now come to the function calls,

1^st function call:

A = sum(5);

Here, X = 5 and Y =10, because the value of K is 10 till now. then function return 15. 

2^nd function call:

A = sum(5);

Before the second function call, we modify the value of the global variable K. The new value of K is 20. Then X = 5 and Y =20. Then function sum() return 25.

Then the final output "15 25" will be printed on the console screen.

Program 2:

#include <iostream>
#define NUM 10 + 20
using namespace std;

int fun(int X = NUM)
{
    return (NUM * NUM);
}

int main()
{
    int RES = 0;

    RES = fun();

    cout << RES;

    return 0;
}

Output:

230

Explanation:

Here, we defined function fun() that takes macro NUM as a default value of the argument.

Now, evaluate the expression used in the return statement,

NUM*NUM
10+20*10+20
10+200+20
230

Then function fun() will return 230, and that will be printed on the console screen.

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