This header file defines various operations on characters. The various character functions available in C++. The header file ctype.h is to be included to use these functions in a program

The scope operator reveals the hidden scope of a variable. The scope resolution operator (::) is used for the following purpose. To access a Global variable when there is a Local variable with same name.

The general syntax of a function definition is:
Return_Data _Type Function _ name (parameter list)
{
Body of the function
}

The srand() function in C++ seeds the pseudo random number generator used by the rand() function. The seed for rand() function is 1 by default. It means that if no srand() is called before rand(), the rand() function behaves as if it was seeded with srand(1). The srand() function takes an unsigned integer as its parameter which is used as seed by the rand() function. It is defined in < cstdlib >or< stdlib.h >header file.

int r=isalnum('5');
cout << isalnum('A') << '\t' << r;
But the statements given below assign 0 to the variable n, since the given character is neither an alphabet nor a digit.
charc = '$';
int n = isalnum(c);
cout << c;
Output:
0

Function gets() reads a string' from standard input and stores it into the string pointed by the variable. Function puts() prints the string read by gets() function in a newline.

The predefined function getchar() is used to get a single character from keyboard and putchar() functions is used to display it.

getchar(), putchar(), gets(), puts()

stdio.h is a header file contains pre-defined "standard input/output" functions

Data types and constants used with the library functions are defined in them

(i) A local variable is defined within a block. A block of code begins and ends with curly braces { }.
(ii) The scope of a local variable is the block in which it is defined.
(iii) A local variable cannot be accessed from outside the block of its declaration.
(iv) A local variable is created upon entry into its block and destroyed upon exit

Arguments or parameters are the means to pass values from the calling function to the called function. The variables used in the function definition as parameters are known as formal parameters. The constants, variables or expressions used in the function call are known as actual parameters.
Types : Default arguments and Constant Arguments.

Void type has two important purposes:
(I) To indicate the function does not return a value
(ii) To declare a generic pointer

The strelen() takes a null terminated byte string source as its argument and returns its length. The length does not include the null(\0) character.

A large program can typically be split into small subprograms (blocks) called as functions where each sub-program can perform some specific functionality. Functions reduce the size and complexity of a progrann, makes it easier to understand, test, and check for errors.