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csH-JavaX-2021
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crypto

Instructions


aim

to produce an encrypted message from an original plain text message
use (int) and (char) to convert between character and integer values

remember that each character in a String has a position number starting at 0 and finishing at 1 less than the length of the string

key idea `charAt()` function

"Computer".charAt(2) would produce the character at position 2
the charAt() function returns a char value, not a String
'A' is a character, "A" is a String

key idea (char) & (int) casting

Each character value has a matching integer value in the ASCII table, 'A' is 65
this means it is possible to convert from one datatype to the other, this is called casting in Java.
it is also possible to do some arithmetic operations on characters!

Steps PRIMM


PREDICT-RUN

Read the PREDICT-RUN code
Share with a partner what you think will be displayed by the code, try to give reasons.

INVESTIGATE and MODIFY

try different letters from the alphabet string: start, middle and end. How will you do this?
try different shift values, 0, 1-25, 26, over 26, negative values? How will you do this?

MAKE

uncomment the loop code in the `MAKE` section and run the program to see what it does
create code to encrypt the entire message, use code in the `PRIM` section above
⁠

challenge using an IF construct

Any characters in the message which are not in the alphabet should not be encrypted.
loop with index from 0 to length of string -1
letter is char at index position
if letter is between A and Z
letter is char at index position shifted by cipher distance
end if
display letter
end loop
The code could also be able to handle lower case letters.
Instructions
aim
key idea `charAt()` function
key idea (char) & (int) casting
Steps PRIMM
PREDICT-RUN
INVESTIGATE and MODIFY
MAKE
challenge using an IF construct
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