is there a range for ascii values ?

Answer 1

0 to 127. Standard ASCII is for 7-bit characters, and 0 to 127 are the values that can be represented in 7 bits.

Some of those values (those less than 32 which are control characters, and 127 which is DEL) tend not to print as a single character. If you want to know about printable single characters, they're 32 (space) through 126 (tilde) inclusive, for 95 characters.

See:
http://www.asciitable.com/

Answer 2

Yes there is small letters-32=capital letters...so on.it like normal maths.they are in arithmetic progression.