You do not need to convert characters to a number. It is a matter of interpretation of your data.
Charater 'A' can be thought of 0x41 or 65 so this is perfectly fine:
int number = 'A';
and value on variable number is 0x41/65 or 1000001b depending how you want to present it/treat it.
As for interpretation : 0xFF may be treated as 255 if you present it as unsigned value or even as -1 when treated as signed and kept in 8 bits.
So your question:
can convert a string into ASCII values?
is kind of wrong - all characters of the string are already ascii values - it is just a matter of how you treat/print/interpret/present them.