Попробуйте следующее:
NSURL *url = [NSURL URLWithString:@"http://www.arijasoft.com/givemesomthing.php?a=3434&b=435edsf&c=500"];
NSMutableString *parameterString = [NSMutableString stringWithFormat:@"{%@;}",[url parameterString]];
[parameterString replaceOccurrencesOfString:@"&" withString:@";"];
// Convert string into Dictionary
NSPropertyListFormat format;
NSString *error;
NSDictionary *paramDict = [NSPropertyListSerialization propertyListFromData:[parameterString dataUsingEncoding:NSUTF8StringEncoding] mutabilityOption: NSPropertyListImmutable format:&format errorDescription:&error];
// Now take the parameter you want
NSString *value = [paramDict valueForKey:@"c"];