ReverseString.m

  // Cadena original
  NSString *cadena = @"El DevF rockea";
  // Cadena invertida 
  NSMutableString *reverse = [[NSMutableString alloc] init];
  
  int time = 0;
  
  for (int i = (int)([cadena length] - 1); i >= 0; i--) {
      NSRange subString = NSMakeRange(i, 1);
      
      // Verifica si contiene la letra E o e en cadena             
      time += ([[cadena substringWithRange:subString]  isEqual: @"e"] || [[cadena substringWithRange:subString]  isEqual: @"E"]  ) ? 1 : 0;
      
      [reverse appendString:[cadena substringWithRange:subString]];
  }
  
  NSLog(@"%@", reverse);
  
  NSLog(@"%d veces", time);