I think your calculation is wrong: You currently have encryptedLetter = (letter – firstLetterOffset) + key[position % keyLength] % 26 + firstLetterOffset by check the C operator precedence table we notice that % is evaluated before – or +, meaning that your code actually mean : encryptedLetter = (letter – firstLetterOffset) + ( key[position % … Read more
Your code: if (Char.IsLetter(s[i])) { s[i] = (char)(s[i] + key[j] – ‘A’); if (s[i] > ‘Z’) s[i] = (char)(s[i] – ‘Z’ + ‘A’ – 1); } Depends on the fact that the letters from U+0041 to U+005A just happen to match a the letters of the alphabets of some languages, such as English*. (If the … Read more
There are several problems with your code: You’re error checking isn’t correct. You check if(argc!=2||!apha) after you’ve already evaluated strlen(argv[1]) — by then it’s too late! Check the validity of argc before accessing argv and don’t double up the argument count error and alphabetic key error, they’re independent. Also, error messages should go to stderr, … Read more