What is a string?     
  
A string is a group of  characters ended with null character. It is also known as array 
  of characters. 
  
  Declaration 
  
  char name_of_the_string; 
  
  where name of the string must be valid  identifier & size must be an integer constant 
  
  Most useful functions available inside string.h header file 
  
 
 
strcpy() 
This function copies one string into another string. 
Format: strcpy(s1,s2) 
where s1 is a string variable and s2 is a string variable or string constant. 
  
e.g. strcpy("Hello",s1); 
will copy Hello to string variable s1. 
  
 
strlen() 
It counts the number of characters including null in the  given string. 
  e.g. cout<<strlen("c++"); 
  Output: 4 
  
  
         
strcmp() 
Format: strcmp(s1,s2); 
  
This function will return 0 if two strings are equal, -1 if  1st string is smaller than 2nd and 1 if 1st string is greater than 2nd 
  This function is case sensitive & compares two strings by ASCII value of  the characters. 
  
  
             
 strrev() 
It prints given string into its reverse order 
  e.g. cout<<strrev("abc"); 
  Output: cba 
  
  
         
strcat() 
This function add two strings. 
  Format: strcat(s1,s2) 
  e.g. cout<<strcat("abc","xyz"); 
  Output:abcxyz 
  
  
         
strupr() 
It converts given string in uppercase. 
  Format: strupr(s1) 
  where s1 can be a string variable or a string constant.  
  
  
  
         
strlwr() 
It converts given string in lowercase. Format is same as  that of strupr(). 
  
  
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