1. Strings

2. Declaring Strings
strings are specific constructs that are designed for processing sequences of characters
before using, include string header: #include <string> don’t use string.h
as well as using std::string;
string declaration: string mystr;
value assignment at declaration:
string mystr(”Hello”);
string mystr2=”Hello”;
assignments from other types are not permitted:
string error1 = ’c’; // error
string error2 = 22; // error
can assign a character with assignment operator: mystr=’n’;

3. String I/O string can be output as any other type:
string s=”hello world”;
cout << s << endl;
two ways to input strings:
using extraction operator - strips white space and assigns the first token (word) to the string:
cin >> s;
hello world\n input assigns only hello to s
using getline function - assigns all characters to string up to newline (not included, \n is discarded):
getline(cin, s);
hello world\n input assigns hello world to s
to successfully mix getline and extraction, may need
cin.peek() – returns next character without removing
cin.get() – returns a single next character
cin.unget() – puts previously returned character back into cin
cin.peek() returns the next character without removing
cin.get() returns the next character
cin.unget() puts it back

4. String Assignment and Concatenation
use assignment operator as with other types:
string s1, s2, s3;
s1=”C++”;
s2=”fun”;
plus “+” is used for string concatenation: s3=s1 + ” is ” + s2;
at least one operand has to be string variable!
compound concatenation allowed: s1 += ” language”;
characters can be concatenated with strings:
s2 = s1 + ’o’;
s2+=’o’;
no other types can be assigned to strings or concatenated with strings:
s2= 42.54; // error
s2=”Catch” + 22; // error

5. Comparing Strings
comparison operators (>, <, >=, <=, ==, !=) are applicable to strings
strings are compared lexicographically:
string s1=”accept”, s2=”access”, s3=”acceptance”;
s1 is less than s2 and s1 is less than s3
the following rules hold:
letters in the alphabet are in the increasing order
longer word (with the same characters) is greater than shorter word
comparison to literal string constants and named constants is also legal:
const string myname=”John Doe”;
string hername=”Jane Doe”;
if ((myname==hername)||(myname==”Jake Doe”))
cout << ”found him\n”;

6. String Functions String Characteristics
a number of standard functions are defined for strings. Usual syntax:
string_name.function_name(arguments)
useful functions return string paremeters:
size() - current string size (number of characters currently stored in string
length()- same as size()
max_size() - maximum number of characters in string allowed on this computer
empty() - true if string is empty
example:
string s=”Hello”;
cout << s.size();
outputs 5

7. Accessing Elements of Strings
similar to arrays a character in a string can be accessed and assigned to using its index (start from 0)
cout << str[3];
it is an error to access an element beyond the size of the string:
string s=”Hello”; // size is 5
cout << s[6]; // error
the type of the element of the string is character, assigning integers, strings and other types are not allowed
s[3] = ”hi”; // error
s[3] = 22; // error

8. Substrings, Searching
substr - function that returns a substring of a string: substr(start, numb) start - index of the first character, numb - number of characters
string s=”Hello”; // size is 5
cout << s.substr(3,2); // outputs ”lo”
find family of functions return position of substring found, if not found return global constant string::npos defined in string header
find(substring) - returns the position of the first character of substring in the string
rfind(substring) - same as find, search in reverse
find_first_of(substring) - find first occurrence of any character of substring in the string
find_last_of(substring) - find last occurrence of any character of substr in the string
all functions work with individual characters as well:
cout << s.find(’l’);

9. Searching for All
all search functions work with a particular starting position
find(substring, startingPosition)
example: reporting all occurrences of character ‘a’
string s= ”baa baa black sheep”;
int pos=s.find(’a’);
while (pos != string::npos){
cout << ”found a at ” << pos << endl;
pos=s.find(’a’, pos+1); }

10. Inserting, Replacing
insert(start, substring)- inserts substring starting from position start
string s=”place”;
cout << s.insert(1, ”a”); //produces ”palace”
variant insert(start, number, character) – inserts number of character starting from position start
cout << s.insert(4, 2, ’X’); //produces ”placXXe”
note it is a character not a string
replace (start, number, substring)- replaces number of characters starting from start with substring the number of characters replaced need not be the same
string s=”Hello”;
s.replace(1,4, ”i, there”); //produces ”Hi, there”

11. Appending, Erasing
append(string2)- appends string2 to the end of the string
string s=”Hello”;
cout << s.append(”, World!”);
cout << s; // outputs ”Hello, World!”
erase(start, number)- removes number of characters starting from start
s.erase(1,2);
cout << s; // outputs ”Hlo”
other useful functions s.clear()  empties the string
s.resize(50)  changes size to specified, either truncating or extending with null characters

12. Passing Strings as Parameters Returning Strings
strings can be passed as parameters:
by value:
void myfunc(string s);
by reference:
void myfunc(string &s);
if string is not modified by function use const type modifier:
void myfunc(const string &s);
strings (unlike arrays) can be returned:
string myfunc(int, int);
note, that passing strings by value and returning strings is less efficient than passing them by reference