Characters

Character Types in C

There are char, signed char, and unsigned char as character types

The implementation defines char to have the same behavior as either signed char or unsigned char

• Check the <limits.h> file, if CHAR_MIN is 0, it is unsigned, otherwise signed.

All char types are 1 byte, no issues with ordering bytes

ASCII Encoding

ASCII is a codebook that maps bit patterns 0x00 through 0x7F to control characters and printable characters.

• Range is known as the codespace
• Each pattern is called a code point
• ASCII encodes 128 values (MSB always 0)

Important codes:

• Ox00 or \0 for NUL (not to be confused with the NULL pointer, which is word size length), this is 1 byte
• 0x20 for ’ ’ (whitespace)
• 0x7F for DEL

Codebook

Operations on Characters

Characters are literally just integer types, so you can perform arithmetic operations on them.

Example: atoi()

atoi() is part of the standard C library, and provides a way of converting ASCII to Integer (hence the a-to-i name).

atoi("429") would return 429

int atoi(const char[s]) { // const tells us the parameter array cannot change
	int retval = 0;
	for(int i = 0; s[i] != '\0'; i++) {
		retval *= 10;
		retval += s[i]-'0';
	}
	return retval;
}

Other representations

There are other representations for characters as well, namely Unicode.