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In the preceding line, we have included the iostream.h header file. Now, you can use all the
functions defined in the iostream.h header file in your program. You can also use “” (double
quote) in place of angular brackets. The use of angle brackets < > instructs the compiler to
search the compilers include directory for the specified header file. On the other hand, the use
of the double quote “ “ instruct the compiler to search in the current directory for the specified
header file.
Let us use some of the library functions to understand the concepts better.
Functions of ctype.h Header File
The ctype.h header file contains the definitions of character handling functions. You need to
include this header file in your program to use the character functions. Some of the commonly
used functions of the ctype.h header file are:
Function Name Use Example Output
isalpha(char c) It returns true if the character c is an isalpha(‘B’) True
uppercase or a lowercase letter. Otherwise
returns false.
islower(char c) It returns true if the character c is a lowercase islower(‘B’) False
letter. Otherwise returns false.
isupper(char c) It returns true if the character c is an isupper(‘B’) True
uppercase letter. Otherwise returns false.
isdigit(char c) It returns true if the character c is a digit isdigit(‘9’) True
from 0 through 9. Otherwise returns false.
isalnum(char c) It returns true if character c is a digit from isdigit(‘$’) False
0 through 9 or a letter either uppercase or
lowercase. Otherwise returns false.
tolower(char c) It converts the character c to lowercase if isupper(‘B’) b
it is in uppercase. Nothing will change if
the character is a lowercase letter or a non-
alphabetic character.
toupper(char c) It converts the character c to uppercase if it isupper(‘b’) B
is in lowercase. Nothing will change if the
character is an uppercase letter or a non-
alphabetic character.
Program 1: To use character handling functions.
#include<iostream.h>
#include<ctype.h>
#include<conio.h>
void main()
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