stringByReplacingCharactersInRange: withString: 實現字符串删除，替换

NSString *str = @"1234567890"; [str stringByReplacingCharactersInRange:NSMakeRange(str.length-1, 1) withString:@""];NSLog(@"str = %@",  str);  // str = 123456789

 [str stringByReplacingCharactersInRange:NSMakeRange(str.length-1, 1) withString:@"1"];

解释：NSMakeRange(str.length-1, 1),将字符串str定位到第九个字符即‘9’，取长度为1的字符串，即9后第一个字符串 ‘0’，用字符串@“”替代‘0’，即所得的结果为“123456789”

NSString *str = @"1234567890"; [str stringByReplacingCharactersInRange:NSMakeRange(str.length-2, 2) withString:@"aa"];NSLog(@"str = %@",  str);  // str = 12345678aa