1. The scope operator reveals the hidden scope of a variable. The scope resolution operator (::) is used for the following purposes.
2. To access a Global variable when there is a Local variable with same name. An example using Scope Resolution Operator.

The pow() function returns base raised to the power of exponent. The sint) function takes a single argument in radians.
#include < iostream >
#include < math.h >
using namespace std;
int main ( )
{
double base, exponent, result;
base = 5;
exponent = 4;
result = pow(base, exponent);
cout < < "pow("< < base < <"˄" < < exponent < <") =" < < result;
double x = 25;
result = sin(x);
cout < < "\nsin("< < x < <")=" < < result;
return 0;
}
Output:
pow(5^4) = 625
sin(25)= -0.132352

This function is used to check whether a given character is a digit or not. This function will return 1 if the given character is a digit, and 0 otherwise.
Example:
using namespace std;
#include< iostream >
#include< ctype.h >
int main( )
{
char ch;
cout < < "m Enter a Character:";
cin > > ch;
cout< < "\n The Return Value of isdigit(ch) is :"<< isdigit(ch);
}
Output-1
Enter a Character: 3
The Return Value of isdigit( ch) is :1
Output-2
Enter a Character: A
The Return Value of isdigit(ch) is :0

Divide and Conquer
1. Complicated programs can be divided into manageable sub programs called functions.
2. A programmer can focus on developing, debugging and testing individual functions.
3. Many programmers can work on different functions simultaneously.

In C++, one can assign default values to the formal parameters of a function prototype. The Default arguments allows to omit some arguments when calling the function.
When calling a function,
For any missing arguments, complier uses the values in default arguments for the called function.
i. The default value is given in the form of variable initialization.
Example: void defaultvalue(int n1-10. n2=100);
ii. The default arguments facilitate the function call statement with partial or no arguments.
Example: defaultvalue(x,y);
defaultvalue(200,150);
defaultvalue(150);
defaultvalue(x,150);
iii. The default values can be included in the function prototype from right to left, ie, we cannot have a default value for an argument in between the argument list.
Example: void defaultvalue(int n1-10, n2);//invalid prototype
void defaultvalue(int n1, n2 = 10);//valid prototype

(i) The return value of the function is of type long.
(ii) fact is the name of the function.
(iii) The function is called with two arguments:
The first argument is of int data type.
The second argument is of double data type. 
int display(int, int) // function prototype
The above function prototype provides details about the return data type, name of the function and a list of formal parameters or arguments.

The pow() function returns base raised to the power of exponent. If any argument passed to pow() is long double, the return type is promoted to long double. If not, the return type is double. The pow() function takes two arguments.
(i) base- the base value
(ii) exponent - exponent of the base
Example :
cout <<pow(5,2);
output
25

The strcmp () function takes two arguments: string 1 and string 2. It compares the contents of string 1 and string 2 lexicographically.
The strcmp() function returns a:
(i) Positive value if the first differing character in string 1 is greater than the corresponding character in string 2. (ASCII values are compared).
(ii) Negative value if the first differing character in string 1 is less than the corresponding character in string 2.
(iii) 0 if string 1 and string 2 are equal.

C++ provides a rich collection of functions ready to be used for various tasks. The tasks to be perfornned by each of these are already written, debugged and compiled, their definitions alone are grouped and stored in files called header files. Such ready-touse sub programs are called pre-defined functions or build-in functions.