The word “conic" stands for console input/output. The “conio” header file contains various basic input and output built-in functions. Some commonly used functions of this header file are as follows:

What is clreol() Function

The word “clreol” is the short of clear end-of-line. The clreol() function is used to clear a line from the current cursor position up to the end of line. The other text printed on the screen is not cleared.
The declaration of clreol() function is as follows:

  void clreol (void);

The declaration of this function indicates that no parameter is passed to this function. This function returns no value.
The general syntax to call clreol() function is as follows:

clreol () ;

Example Program of clreol() Function

#include 

main ()

{

   gotoxy (0, 9);

   clreol();

}

The declaration of kbhlt() function is as follows:

  int kbhit (void);

indicates that no parameter is passed to this function. The output returned by this function is ‘int’ type. It returns non-zero value if keyboard is hit by the user, otherwise returns 0. The general syntax to call kbhit() function is as follows:

  [ var = ] kbhit();

To clear the concept of kbhit() function, read the given below example program.
The kbhit() Function Example Program
(A program that displays a message on the screen repeatedly until a key on the keyboard is hit.

#include
#include
main ()
{
   int r = 1;
   clrscr();
   while ( !kbhit() )
   {
     cout     gotoxy(25, r);
     clreol();
     r++;
     if ( r== 24) r=1;
    }
getch();
}

The gotoxy() function is used to move the cursor to the specified location in the current text window. This function is normally used when an output is to be displayed on a specified location on the screen. 

void gotoxy (int, int);

gotoxy (4, 15);

cout

The word “stdio” stands for standard input/output. This header file contains various standard input and output functions. These functions are used to get input from the input device and to print/display the output on the output device. The most important and commonly used functions of 'stdio.h' header file are as follows:

1. getchar
2. putchar
3. puts
4. gets

What is getchar() Function? 

The word "getchar" is the short of get character. The getchar() function is similar to "getche" function of "canio.h" header file. It is also used to get a single character from a standard input device (i.e from keyboard) during program execution.
The main difference between getche() and getchar() function is that when getchar() function is used then we must have to pass Enter key to complete the input process.
The declaration of getchar() function is as follows:
Thet general syntax to call getchar() function is given below:-
Note: The use of [var =] is optional. 

char: It represents the character to be displayed on the screen. It may be a character variable or character constant. In case of character constant, the character is enclosed in single quotation marks.

What is gets() Function?

The word "gets" stands for get string. The gets() function is used to input (or get) data into a string variable from the keyboard during program execution. Any type of characters, including spaces and special characters can be entered using this function. Enter key is pressed to complete the input process. When Enter key is pressed, a null character ('\0') is automatically added at the end of the string variable.
The general syntax to call gets() function is as follows:
In the above syntax:-
strvar: It represents the string variable into which data is to be saved.

Note: We can also input data into a string using "cin" stream object but space character can't be interested into the string using the "cin" stream object. When a space key is pressed during input process, the "cin" object immediately appends the null character ('\0') at that place in the string variable. Therefore, gets() function is specifically used to get data into string variable.

Functions Under "ctype" Header File

What is isalpha() Function

In C++, the isalpha() function is used to check whether a given character is alphabet latter or not. This function returns no-zero value (true value in the form of 1) if the given character "A" to "Z" or "a" to "z". Otherwise, this function returns 0 in the case of digits, special characters or any other data types.

The general syntax in C++ to call isalpha() function is as follows:

var = isalpha(c);

where:

c	It represents a single character or ASCII value for a character.
var	It indicates the integer variable into which the returned value is to be assigned.

Example Program of isalpha() Function

#include 
#include
#include 
int main ()
 {
   int i=0;
   char str[]= "C++" ;
   clrscr();
   while (str[i])
 {
   if (isalpha(str[i]))
 coutelse
 cout i++;
}
getch();
}

What is isalnum() Function

The isalnum() function is used to check whether the given character is alphanumeric character or not. This function returns a non-zero (true value) if the given character is alphabetic letters and numeric digits ( 'A' to 'Z' or 'a' to 'z' and '0' to '9' ). In the other case, this function returns 0.

Syntax of isalnum() Function

In C++, the general syntax to call isalnum() function is as follows:

var = isalnum(c); 

Where:
For example: 
If c = '5' then isalnum(c) will return 1 (non zero value).
If c = '&' then isalnum(c) will return 0.

What is isdigit() Function

The isdigit() function is used to check whether the given character is numeric digit or not. This function returns true value (non zero) if the given character is '0' to '9'. Otherwise, this function returns 0.

Syntax of isdigit() Function

In C++, the general syntax to call isdigit() function is as follows:

var = isdigit(c);

Where:
For example:
If c = '7' then isalnum(c) will return  1 (non zero value).

What is isxdigit() Function

The isxdigit() function is used to check whether the given character is hexadecimal digit or not. This function returns true value (non zero) if the given character is '0' to '9', 'A' to 'F' or 'a' to 'f'. Otherwise, this function returns 0.

Syntax of isxdigit() Function

In C++, the general syntax to call isdigit() function is as follows:

var = isxdigit(c);

Where:
For example:

• If c = 'A' then isxdigit(c) will return  1 (non zero value). 
• if c = 'Z' then isalnum(c) will return 0.

What is islower() Function

The islower() function is used to check whether the given character is a lowercase letter or not. This function returns non-zero value (true value) if the given character is 'a' to 'z'. Otherwise, this function returns 0.

Syntax of islower() Function

In C++, The general syntax to call islower() function is as follows:

var = islower(c);

Where:
For example:
If c = 'g' then islower(c) will return true value (1).

What is tolower() Function

In C++, the tolower() function is used to convert the given uppercase letter (A to Z) to lowercase (a to z) letter.

Syntax of tolower() Function

The general syntax to call tolower() function is as follows:

var = tolower(c);

Where:
For example:

• If c = 'y' then tolower(c) will return letter "Y". 
• if c = 'a' then tolower(c) will return letter "a".

What is isupper() Function

The isupper() function is quite opposite to the islower() function. This function is used to check whether the given character is a uppercase letter or not. This function returns non-zero value (true value) if the given character is 'A' to 'Z'. Otherwise, this function returns 0.

Syntax of isupper() Function

In C++, The general syntax to call islower() function is as follows:

var = isupper(c);

Where:
For example:

• If c = 'H' then isupper(c) will return true value (1). 
• if c = 'h' then isupper(c) will return 0.

What is toupper() Function

In C++, the toupper() function is used to convert the given lowercase letter (a to z) into uppercase (A to Z) letter. This function is opposite to the tolower() function.

Syntax of toupper() Function

The general syntax to call toupper() function is as follows:

var = toupper(c);

Where:
For example:

• If c = 'T' then toupper(c) will return letter "T". 
• if c = 'p' then toupper(c) will return letter "P".

What is isascii() Function

The isascii() function is used to check whether the given value is ASCII value or not. This function returns a non-zero value (1) if the given value is '0' to '127'. Otherwise, this function returns 0 (false value).

Syntax of isascii() Function

In C++, the general syntax to call isascii() function is as follows:

var = isascii(c);

Where:
For example:
If c = 127, then isascii(c) will return 1 (true value).

What is toascii() Function

In C++, the toascii() function is used to convert a character to ASCII value.

Syntax of toascii() Function

The general syntax to call toascii() function is as follows:

var = toascii(c);

Where:
For example:

• If c = 'A' then toascii(c) will return ASCII value 65. 
• if c = 'a' then toascii(c) will return ASCII value 97.

What is isspace() Function

The isspace() Function is used to check whether the entered value (character) is a space or not. This function returns true (non-zero) value if the given character is space, tab, form feed, carriage return, new line and vertical tab etc. Otherwise, this function returns false (0).

Syntax of isspace() Function

In C++, the general syntax to call isspace() function is as follows:

var = isspace(c);

Where:
For example:

• If c = '  ' then isspace(c) will return true value (1). 
• if c = '/' then islower(c) will return 0.

What is isprint() Function

The isprint() function is used to check whether the given character is a printing character or not. All alphabets, digits, alphanumeric characters including space are printing characters. Space, new line, carriage return, tab, form feed and all other escape sequence characters are not printing characters.
The isprint() function returns true (1) if the given character is a printing character. Otherwise, this function returns false (0) in the case of space, new line, carriage return, tab, form feed and all other escape sequence characters.

Syntax of isprint() Function

The general syntax to call isprint() function is as follows:

var = isprint(c);

Where:
For example:
If c = 'e' then isprint(c) will return true value (1).

What is iscntrl() function

The iscntrl() function is used to check whether the given character is a control character or not. The new line ("\n"), carriage return ("\r"), form feed ("\f") etc. are control characters. It means that all escape sequence characters are control characters. This function returns true (1) if the given character is a control character. Otherwise, this function returns 0.

Syntax of iscntrl() Function

The general syntax to call iscntrl() function is as follows:

var = iscntrl(c);

Where:
For example:
If c = '\n' then isprint(c) will return true value (1).
if c = '$' then isprint(c) will return 0.

Functions Under "math" Header File

What is cos() Function?

The cos() function is used to find the trigonometric cosine of a given angle. The angle is given in radian as a real number. The declaration of cos() function is as follows:
The declaration of cos() function indicates that a single parameter of "double" type is passed to this function. The output returned by cos() function is also of "double" type.
The general syntax to call the cos() function is as follows:

var = cos(x);

In the above syntax:
x: It indicates the angle in radian. It may be a variable, a constant or an expression.
y: It indicates the variable into which the returned value is to be assigned.


For example, if x = 0.0, then cos(x) will return 1.0

What is fmod() Function?

The word "fmod" is the short of "for floating-point modulus". The fmod() function is used to find the remainder by dividing two real numbers. The declaration of fmod() function is as follows:
The general syntax to call fmod() function is as follows:
In the above syntax:
x: It indicates the numerator. It may be a variable, constant value or expression.
y:It indicates the denominator. It may be a variable, constant value or expression.
var: It indicates the variable of "double" type into which the returned value is to be assigned.
For example, if x = 9.5 and y = 4.0 then fmod(x, y) will return 1.5.

What is strlen() Function

The word "strlen" is the short of string length. The strlen() function is used to find out the length of a string. This function counts the total number of characters in the string including spaces. But, the null character ('\0') is not counted.
In C++, the general syntax of strlen() function is as follows:

var = strlen (string);

Where:

Example of strlen() Function

The following source code of the C++ program inputs a string variable and finds its length using strlen() function.

#include
#include
#include
main()
 {
   char str[200];
   cout   gets(str);
   cout   return 0;
 }

Output:
Enter a string: C++ Tutorials
Length of string is: 13

What is memcmp() Function

The word "memcmp" is the short of memory compare. In C++, the memcmp() function is used to compare specified number of bytes of two strings stored in two blocks of memory. Two strings are compared by "byte-by-byte" in this function. The comparison is case sensitive, it means that this function keep difference between lowercase and uppercase letters of the string.
The general syntax of this function is:

var = memcmp (ptr1, ptr2, num);

Where:

The memcmp() function returns output in the following ways:

• If first string is equal to the second string, then it will return 0.
• If first string is less than second string, then it will return less than 0.
• If first string is greater than second string, then it will return greater than 0.

Example of memcmp() Function

The following source code of C++ program compare two strings.

#include
#include
using namespace std;
main()
 {
   char *str1 = "abcd";
   char *str2 = "abcd";
   char *str3 = "wxyz";
   int num;
   num = memcmp (str1, str2, 3);
   if (num == 0)
          cout   num = memcmp (str2, str3, 3);
   if (num > 0)
          cout   else
          coutreturn 0;
}

What is memicmp() Funaction

The word "memicmp" is stands for memory ignore compare. This function is similar to memcmp() function but here the comparison is not case sensitive. Its mean that memicmp() function ignores the character case (lower or upper). It is also used to compare specified number of bytes (or characters) of two strings stored in two memory blocks.
In C++, the general syntax of this function is as follows:

var = memcmp (ptr1, ptr2, num);

Where:
The memicmp() function returns output in the following ways:

• If first string is equal to the second string, then it will return 0.
• If first string is less than second string, then it will return less than 0.
• If first string is greater than second string, then it will return greater than 0.

Example of memicmp() Function

The following source code of C++ program compare two strings.

#include
#include
using namespace std;
main()
 {
   char *s1 = "abcd";
   char *s2 = "ABCD";
   char *s3 = "wxyz";
   int num;
   num = memcmp (s1, s2, 3);
   if (num == 0)
          cout   num = memcmp (s2, s3, 3);
   if (num > 0)
          cout   else
          coutreturn 0;
}

The memcmp() and memicmp() both functions are similar, the main difference is that memcmp() function is case sensitive (keep difference between lower and upper case letters). Whereas the memicmp() function doesn't keep difference between lower and upper case letters.

Functions Under "graphics" Header File

In graphics mode, text can also be displayed in different fonts, styles, sizes, colors and directions. The graphics functions that are commonly used to create and print text are as follows:

1. outtext
2. moveto
3. Tlie outtextxy
4. settextstyle 
5. setcolor
6. setbkcolor