Default value

This is the difference between CPP and C.

When defining a function, you can specify a default value for each of the last parameters.

int sum(int a, int b=10){
    return a + b;
}

Overloading

This is the difference between CPP and C.

Function overloading allows to create multiple functions with the same function name, so long as they have different argument list (the types and/or the number of arguments).

int sum(int a, int b=10){
    return a + b;
}
float sum(float a, float b=10){
    return a + b;
}

You can not overload function declarations that differ only by return type. The following declaration results in an error.

int printName(int a) {}
float printName(int b) {}