Question

Can someone please break down this code for me? I know it changes text from a user file and I know it could be very useful to me. What is the purpose of “~”? How could I amend this code to read a user file word by word and then change it using the same kind of formula?

// first value in the file is the key
if ( fread(&key, sizeof(char), 1, infile) )
{ 
    key = ~key;  
}
while( fread(&fval ,sizeof(short), 1, infile) )
{
      fputc( (fval / 2) - key, outfile );  
} 

Answer 1

key = ~key swaps all the bits of key

You know about bits?

ascii A (65) is 100 0001 in binary, so ‘~’ of this is simply swaps each 1 for 0 and each 0 for 1 giving 011 1110 (62) which is >

So this will replace all the As in your document with > and similarly for every other character. The nice thing about ~ is that it’s exactly the same process to decrypt – just swap each bit back.

ps. It’s not exactly mil-spec encryption!