Homework 1, Notes

• (type) expression is from c, and is not great.
• type(expression) is from early c++, and is ok, but not sufficient for modern usage
• xxx_cast<type>(expression) is a family of casting operations. XXX can be static, dynamic, cost, reinterpret.
• For now, please use static_cast.

• These functions will convert a single alpha character to the required case. They will ignore non-alpha characters.
• See page 123 of your book.
• We will discuss this further soon.

• These functions return true if a single alpha character is upper or lower.
• We will discuss this further soon.

• Checks to see if a letter is alphabetic.
• We will discuss this further soon.

• This returns the character at position i in the string message or a reference to that character (More on this later).
• It is very close to the .at function (see page 123) but it does no range checking.
• We will discuss this further soon.
• The [] are an operator (like +, =, and ++) they have this specific purpose and you can not use () do accomplish this (that works in BASIC I believe).

• This is a typedef of an unsigned integer type (int or short probably)
• It is the return value for many "size" type functions (like message.size() or message.length())
• It is the parameter type for many access functions (like message.at());
• See this reference

• \ is the escape character in a string.
• """ is a syntax error.
• "\"" is a string that contains a the quotation character.
• It is also used for non-printable characters like
  • \n end of line character
  • \t tab

char ShiftCharacter(char c){
	bool upper = false;

	if (isalpha(c)) {
		if (isupper(c) ) {
			upper = true;
			c = static_cast(tolower(c));
		}

		c = static_cast (c+SHIFT);
		if (c > 'z') {
			c = static_cast (c-26);
		}

		if (upper) {
			c = static_cast(toupper(c));
		}
	}
	return c;
}
     

• Line 4 determines if the character is a alphabetic character, we do not encrypt non-alphabetic characters.
• Lines 5-8 determine if the character is upper case. We want to preserve upper case, but it is easier to encode if everything is the same case.
• Lines 10-13 shift the character by SHIFT letters in the alphabet. This is a circular shift, so z will wrap around to to c.
• Lines 15-17 restore the case of the original letter.

• This does the circular shift.
• If the character is beyond z, we need to move it back into the alphabet.
• This works based on the ascii table.
• We will discuss this further in class.