C++ strings You have a string class available to you in C++ and can access it using #include<string>  (Note that it is not <cstring>.  cstring is for C style strings which are different as follows: C string - null terminated C++ string - not null terminated.  they contain… pointer to character array length of string  (properties same as what we have been doing Note that when you declare a C++ string you use all lowercase characters ( string NOT String ). There are many things you can do with C++ strings.  For example: Declaration and Assignment examples: string s;                    // empty string with length of 0 string s1 = "Hello";     // can initialize as array of characters string s2 = s1;          // can initialize to another string comparison operators ( ==, !=, <, >, <=, >= ).  All will return bool. examples: string s3; cin >> s3; if (s3 == "sort")      …do sort routine else if (s3 == "print")      … do print routine Multiple Constructors available examples: string s4(7,'a');               // makes string = "aaaaaaa" string s5 = "Frodo";          // uses C style string string s6 = s5; string s7(s5, 3, 2);          // result will be "do" s7 will use s5, starts at element 3, goes length of 2.  Remember - always use zero based indexing so just remember ( source, starting point, number of positions) char msg[] = "This is fun!"; string s8(msg+5, 2);          // result is "is" string s9(msg, 5, 3);     // essentially the same thing they will point to the 5th position of msg ("i") and take two characters ("is") This idea of two integer arguments ( position and length ) is common in C++ strings but beware!  This is a common source of errors. operator = examples: string s1,s2; s1 = s2; s1 = "second";     // converts C style string to C++ string s1 = 'a'               // this will convert character to C++ string                     // because s1 is already declared BUT… string s3 = 'b';     // ERROR - can't declare and initialize this way string class functions: .c_str( ) Takes no arguments and returns a pointer to a C style string.  It enables you to access characters in a data array and change them.  The best way to use this is when you need to read, like using atof… example: string s4 = "123.4"; cout << atof(s4.c_str()); This takes s4 and converts it to a C style string and passes it back to atof which converts it to a float which can then be used in calculations. operator[ ] example s4[1]               // will return character #1 ("2") s1[0] = 'X'     // can do but be careful with [] There are two forms of subscript overloading same as in the class we wrote so just use them whenever you normally would operator + you can use for: string + char string + string string += char string += string .append( char ) or .append( string ) This will append to the end of a string.  Use as follows: string s4 = "zig"; s4.append("zag");          // will give you "zig zag" .insert( int, string) can have many forms.  It allows you to place other strings anywhere inside a string. It has the form: .insert(int position, string) Note:  position - start inserting BEFORE this integer position forms of the .insert function: .insert(int pos, string);                    // inserts all of string .insert(int pos, string, int, int)     //from string, starting..., for …chars .insert(int pos, char *)                    // inserts C style string .insert(int pos, char* int)               // int chars of C style string examples of .insert string s1 = "hot dog"; s1.insert(4, "diggety"); cout << s1;          // yields - hot diggety dog string s2 = "slam"; string s3 = "grand"; s2.insert(0, s3);          // will make  "grand slam" s2.insert(0, s3, 2, 4);     // makes "and grand slam" .replace We can also replace substrings within strings (like changing a name in a message that goes out to several people) .replace(position, length, replace_with) you can use a C style string or C++ string in the replace.  It will adjust the string for different length of replacement. examples of .replace string s5 = "High dive!"; s5.replace(5, 4, "jump");                    // "High jump!" s5.replace(5, 4, "interest rate");     // "High interest rate!" s5.replace(5, 4, "sky");                    // "High sky!" .erase(pos, len) Will erase a given number of characters starting at assigned location and adjust length of the string      .erase(position, length); so now… s5.erase(5, 4);          // "High !" .find(string) Returns an integer indicating location of the first occurrence of a string. examples: s6 = "Ooga Booga"; s6.find("Boo");          // will return 5 (case matters!!) s6.find("Book", 3, 1); this will search using the 3rd position of Book for length of 1 character ("k") and will exit when not found. .length( ) and .size( ) Both functions do the same thing and return an integer which is the length of the string. .rfind(string) Does the same as find except it will start from the end of the string and search backwards. example: string s7 = "High road"; s7.rfind("gh")          // returns 2 as the position This is useful if… string s8 = "www.cs.niu.edu"; int p = s8.rfind('.');     // will find the last period and returns value  10 then you can use… s8.replace(p+1, 3, "com");     // makes "www.cs.niu.com" You could also code:      s8.replace(s8.rfind('.')+1, 3, "com"); The second way works but is not a good idea.  You can get into trouble because order of evaluation is not portable.  It may work on the machine you write the code on and not the machine you implement it on.  If  you don't find '.' on the second way you will get a bogus position so it's best to split up the function calls and always do error checking. .empty( ) This function will takes no arguments and returns a bool indicating if the string is empty or not. .substr( ) takes an integer indicating position and a length of characters and returns a string.  It is used to extract a substring within a string. example: string s1 = "submarine"; string s2; s2 = s1.substr(3,3);          // this extracts "mar" additional information: you can also use cout << s4 and cin >> s4 with C++ strings