C++ Default Arguments (Parameters)

In C++, default arguments allow a function to have default values for one or more of its parameters. If a value is not provided for a particular parameter, the default value is used instead. This can be useful for reducing the number of different versions of a function that need to be written.

Example:

1#include <iostream>
2using namespace std;
3 
4void printNum(int num1, int num2 = 20)
5{
6    cout << "Number 1: " << num1 << endl;
7    cout << "Number 2: " << num2 << endl;
8}
9 
10int main()
11{
12    printNum(10);
13    printNum(30, 40);
14 
15    return 0;
16}

Output:

1Number 1: 10
2Number 2: 20
3Number 1: 30
4Number 2: 40

It is important to note that default arguments must be declared at the end of the function parameter list. This means that all parameters before the default argument must have a value specified when the function is called.

In addition, default arguments are evaluated only once, at the point of function declaration. This means that if the default argument is a variable or a function, its value will be the same for every call to the function.

Example:

1#include <iostream>
2using namespace std;
3 
4int counter = 0;
5 
6void printNum(int num1, int num2 = counter++)
7{
8    cout << "Number 1: " << num1 << endl;
9    cout << "Number 2: " << num2 << endl;
10}
11 
12int main()
13{
14    printNum(10);
15    printNum(30);
16    printNum(50);
17 
18    return 0;
19}

Output:

1Number 1: 10
2Number 2: 0
3Number 1: 30
4Number 2: 0
5Number 1: 50
6Number 2: 0