Easy tutorial for C / C ++ Function 4 (Default argument or default parameter)

Easy tutorial for C / C ++ Function 4 (Default argument or default parameter)

Default argument (default parameter)

- When calling a function, it is usually called according to the number of arguments. However, you can also call it with a different number of arguments using the default parameter.

- Let's look at an example.

Example Code

#include <iostream>

using namespace std;

void defaultP(int a = 3, int b = 30, int c = 300);

int main() {

     cout << endl;

     cout << "##############################" << endl;

     cout << "      Default  parameter      " << endl;

     cout << "##############################" << endl;

     cout << endl;

     cout << " No parameters " << endl ;

     defaultP();

     cout << " 1 parameter " << endl ;

     defaultP(5);

     cout << " 2 parameters " << endl ;

     defaultP(5, 50);

     cout << " 3 parameters " << endl ;

     defaultP(5, 50, 500);

     return 0;

}

void defaultP(int a, int b, int c){

     cout << " a = " << a << ", b = " << b << ", c = " << c << endl;

     cout << endl;

}

- We defined function 'defaultP' with three integer arguments and no return value.

- In the declaration section of the function, the integer variables 'a', 'b' and 'c' are given default values of 3, 30, and 300, respectively.

- In the definition part of the function, there is print statement of 'a', 'b' and 'c' values received as arguments.

- The 'defaultP()' function was called after the output statement "No parameters".

- We will then call the function by incrementing the arguments one by one. At the end, I called the function 'defaultP(5, 50, 500)' after the output statement called "3 parameters".

- Let's check the results.

results :

##############################

      Default  parameter     

##############################

 No parameters

 a = 3, b = 30, c = 300

 1 parameter

 a = 5, b = 30, c = 300

 2 parameters

 a = 5, b = 50, c = 300

 3 parameters

 a = 5, b = 50, c = 500

- " Default parameter " will be displayed first.

(1) "No parameters": Because the function without arguments ( defaultP() ) is called, you can see that the default values are printed.

(2) "1 parameter": Because the function with one argument is called ( defaultP(5) ), the value of the first argument 'a' is changed to 5 and it is printed. At this time, the remaining values are printed to the default values. ("b = 30, c = 300")

(3) "2 parameters": Because the function with two arguments ( defaultP(5, 50) ), you can see that the value of the first argument 'a' and 'b' is  changed to 5 and 50, respectively. The value of the remaining 'c' is set to 300, which is set to the default value.

(4) "3 parameters": Because the function with three parameters ( defaultP(5, 50, 500) ) is called, you can see that it is printed as input value instead of default value.

Note:

1. The value of the default parameter is specified in the declaration part of the function.

2. Give all the default values in the function arguments part, or input sequentially from right to left.

ex) void test(int a=1, int b=2, int c=3); (O)

      void test(int a, int b=2, int c=3);      (O)

      void test(int a=1, int b, int c);          (X)

      void test(int a, int b=2, int c);          (X)