These examples of string manipulation in iPhone apps were taken from the Internet and I don’ pretend on the authority rights for them.

1. Appending string to another string:
   
NSString *myString = @"This";
NSString *test = [myString stringByAppendingString:@" is just a test"];





2. Method with wide possibilities to format string and concatenate several strings:
   
- (NSString*) concatenateString:(NSString*)stringA withString:(NSString*)stringB {
NSString *finalString = [NSString stringWithFormat:@"%@%@", stringA, stringB]; return finalString; }

   
   
   The advantage of this method is that it is simple to put text between the two strings (e.g. Put a “-” replace %@%@ by %@ – %@ and that will put a dash between stringA and stringB




3. String Length:
   
- (int) stringLength:(NSString*)string { return [string length]; //Not sure for east-asian languages, but works fine usually }





4. Remove text from string:
   
- (NSString*)remove:(NSString*)textToRemove fromString:(NSString*)input { return [input stringByReplacingOccurrencesOfString:textToRemove withString:@""]; }





5. Uppercase / Lowercase / Titlecase:
   
   - (NSString*)uppercase:(NSString*)stringToUppercase { return [stringToUppercase upercaseString]; }

   - (NSString*)lowercase:(NSString*)stringToLowercase { return [stringToUppercase lowercaseString]; }





6. Find/Replace:
   
- (NSString*)findInString:(NSString*)string replaceWithString:(NSString*)stringToReplaceWith { return [input stringByReplacingOccurrencesOfString:string withString:stringToReplaceWith]; }





7. String comparison Case Sensitive:
   
if ([category isEqualToString:@"Some String"])
{
doSomething = YES;
}

   
   
   Case Insensitive:
   
if (!([category compare:@"Some String" options:NSCaseInsensitiveSearch]))
{
doSomething = YES;
}


References:

1. http://stackoverflow.com/questions/1778227/string-manipulation-in-objective-c
2. http://www.techotopia.com/index.php/Working_with_String_Objects_in_Objective-C – The best reference on this topic