You can get the string length divide it by desired number and base of it create NSRange:
NSString *str = @"Qwerty";
int len = str.length;
int devider = 2; // Change it to control result length
for (int i = 0; i < len; i += devider)
{
// You should do some validation to make sure your location and length is in range f string length
NSRange ran = NSMakeRange(i, devider);
NSString *res = [str substringWithRange:ran];
NSLog(@"res: %@", res);
}
You can create NSString category to achieve the result you are asking for. Hope this help.