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This is a header file that contains some character conversion and testing functions.

## 1) toupper():

To convert a given lower case English letter into corresponding uppercase letter.
Syntax: d=toupper(c)
Where --> c,d = char

e.g.
c='a' --> d='A'
c='e' --> d='E'
c='G' --> d='G'
c='?' --> d='?'

## 2) tolower():

To convert a given upper case English letter into corresponding lower case letter.
Syntax: d=tolower(c)
Where --> c,d = char

e.g.
c='A' --> d='a'
c='E' --> d='e'
c='g' --> d='g'
c='?' --> d='?'

## 3) isalpha():

To check whether given string contains English letter or not. If yes, then the result is non-zero (true), else 0 (false).
Syntax: d=isalpha(c) --> c is char type, d is int type.

## 4) isdigit():

To check whether given string contains digits or not. If yes, then the result is non-zero (true), else 0 (false).
Syntax: d=isdigit(c) --> c is char type, d is int type.

## 5) isupper():

To check whether given string contains English upper case letters or not. If yes, then the result is non-zero (true), else 0 (false).
Syntax: d=isupper(c) --> c is char type, d is int type.

## 6) islower():

To check whether given string contains English lower case letters or not. If yes, then the result is non-zero (true), else 0 (false).
Syntax: d=islower(c) --> c is char type, d is int type.

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