In order to use string type, we need to include the following code
#include<string> using std::string;
1. Defining and initializing strings
string s1; //Default initialization; s1 is the empty string
string s2(s1); //s2 is a copy of s1.
string s2 = s1; //Equivalent to s2(s1), s2 is a copy of s1.
string s3("value"); //Direct initialization, s3 is a copy of the string literal, not including the null
string s3 = "value"; //Equivalent to s3("value"), s3 is a copy of the string literal.
string s4(n, 'c'); //s4="cccc...ccc", n c
2. Operations on strings
os << s; //Write s onto output stream os. Return os. ex: cout<<s; is >> s; //Reads whitespace-separeted(if it comes across a whitespace, it stops reading) string from is into s. Rreturn is. ex: cin>>s; getline(is, s); //Reads a line of input from is to s. Return is. is can be 'cin' and other types. //getline(cin, s) This function can read a total line, including whitespace. If it comes across the end-of-line, it stops reading. s.empty(); s.size(); //Returns the number of characters in s. If s has whitespace, it still counts. Null character is not included in this size. /* size() doesn't return a int type value. However, it returns a string::size_type value. size_type is a companion type of string. It's an unsigned type. We should be aware that we'd better not to mix int with size_type. */ s1 == s2; s1 != s2; >, <, <=, >= //We can use the strategy as a(case-sensitive) dictionary to compare twos strings. s1 + s2; s1 += s2; /* adding two strings together It won't add a whitespace automatically. s1 = "666", s2 = "777" s3 = s1+s2 = "666777" */ string s1 = "mdzz"; s1 = s1 + "haha"; //1 s1 = "haha" + s1; //2 /* String literals are not standard library strings. Hence, string literals can not be the left-hand operand. 2 is wrong. 1 is ok. */
3. Dealing with the Characters in a string
#include<cctype> //Using this header, we can use many functions to deal with the characters in a string. isalnum(c); //True: c is a letter or a digit isalpha(c); //True: c is a letter iscntrl(c); //True: c is a control character isdigit(c); //True: c is a digit isgraph(c); //True: c is not a space but is printable islower(c); //True: c is a lowercase letter isupper(c); isprint(c); //True: c is a printable character ispunct(c); //True: c is a punctuation character isspace(c); //True: c is a whitespace isxdigit(c); //True: c is a hexadecimal digit tolower(c); toupper(c);