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So far the only form of character information used has been single
characters which are defined as being of type char. Character
strings have also been used in output.
A new data type is now considered, namely, the character
string, which is used to represent a sequence of characters regarded
as a single data item. In C++ strings of characters are held as an
array of characters, one character held in each array element. In
addition a special null character, represented by
`\0', is appended to the end of the string to indicate the end
of the string. Hence if a string has n characters then it
requires an n+1 element array (at least) to store it. Thus the
character `a' is stored in a single byte, whereas the
single-character string "a" is stored in two consecutive bytes
holding the character `a' and the null character.
A string variable s1 could be declared as follows:
char s1[10];
The string variable s1 could hold strings of length up to nine
characters since space is needed for the final null character.
Strings can be initialised at the time of declaration just as other
variables are initialised. For example:
char s1[] = "example"; char s2[20] = "another example"would store the two strings as follows:
s1 |e|x|a|m|p|l|e|\0| s2 |a|n|o|t|h|e|r| |e|x|a|m|p|l|e|\0|?|?|?|?|
In the first case the array would be allocated space for eight characters, that is space for the seven characters of the string and the null character. In the second case the string is set by the declaration to be twenty characters long but only sixteen of these characters are set, i.e. the fifteen characters of the string and the null character. Note that the length of a string does not include the terminating null character.