下面两行代码有什么区别

Question

i am not able to understand why we have to add "a"+randomtext.Next(0,26) for text

buffer[i] = (char)('a' + random.Next(0, 26));

versus

buffer[i] = (char)( random.Next(0, 26));

Answer 1

It is so you have all the letters of the alphabet.

When you pick a number between 0 and 25 and convert it to a char, you will end up with all kind of symbols in the ASCII-Table .

So you add the 'a' which is treated like an int (value is 97) to actually start at the correct position in the ascii-table.

So lets say you random 4.

This line

(char)('a' + random.Next(0, 26));

will be

(char) ('a' + 4)
(char) (97 + 4)
(char) (101) => e

Answer 2

If you don't add 'a', you create an unprintable character. Value of 'a' + random value gives you a printable character

You can look ASCII values at this link : http://www.asciitable.com/mobile/

Answer 3

The ASCII text encoding uses the lower 7 bits of a byte to encode characters. Not all of those characters are visible/printable (such as space, tab, newline, end-of-text, end-of-transmission, etc.).

Lower case letters are encoded as values 0x61 ('a') through 0x7a ('z'). By adding 'a' to your random value you guarantee that you will get one of the lower-case letters. Otherwise you would only get non-printable characters.

Answer 4

Obviously there are issues with this code re 118n but ignoring that for now …

The simple answer to why 'a' was added is to change the range of values placed into the buffer.

The same result may have been accomplished by simply adjusting the two values in the call to random.Next(97,123) etc. but in the interest of making the code understandable, adding the 'a' makes it more obvious what the acceptable range of values was that the coder intended to add to the buffer.