Default Arguments

A parameter can be assigned a default value to be assumed by the corresponding argument when the latter is not specified. 
ClassA(int x = 10)  // x defaults to 10
If only a few parameters of a function have default values, in the function declaration such parameters must appear to the right of those that do not default to any value. 
void func(int x, char y, int z = 14, double d = 21.4);
Only the arguments corresponding to z and d in the code above could be omitted.

Example


#include <iostream>
using namespace std;

class ClassA
{
    int a;
public:
    ClassA(int x = 10)  // x defaults to 10
     {
        a = x;
     }

     void seta(int y)
     {
           a = y;
     }

     int geta()
     {
           return a;
     }
};

int main()
{   
    ClassA obj1;       // the argument defaults to 10
    cout << obj1.geta() << endl; 
    ClassA obj2(21);   // the argument here is specified
    cout << obj2.geta() << endl;
}

Output

10
21