Lecture 19:String Data Type

1. Lecture 19:String Data Type Introduction to Computer Science Spring 2006

2. string Data Type • Programmer-defined type supplied in standard library • A string is a sequence of zero or more characters • Enclosed in double quotation marks • Example: “William Jacob” “Mickey” • Null (empty string): a string with no characters • Example: “” • Each character has relative position in string • Position of first character is 0, the position of the second is 1, and so on • For example, in the string “William Jacob”, the first character, 'W', in name is in position 0, the second character, 'i', is in position 1, and so on • Length: number of characters in string

3. The string Type • To use the data type string, the program must include the header file <string> • The statement: string name = "William Jacob"; declares name to be a string variable and also initializes name to "William Jacob“ • The variable name is capable of storing any size string

4. I/O operations on the string Type • An input stream variable (cin) and extraction operator >> can read a string into a variable of the data type string • Extraction operator • Skips any leading whitespace characters and reading stops at a whitespace character • Should not be used to read strings with blanks • The function getline • Reads until end of the current line • Should be used to read strings with blanks

5. I/O operations on the string Type – Example Assume the input is: Break Back Mountain #include <iostream> #include <string> using namespace std; int main() { string mystring; cin>>mystring; cout<<mystring<<endl; return 0; } #include <iostream> #include <string> using namespace std; int main() { string mystring; getline(cin, mystring); cout<<mystring<<endl; return 0; } Output: Break Output: Break Back Mountain

6. Relational operators on string Type: Comparing string Types • Relational operators can be applied to strings • Strings are compared character by character, starting with the first character • Comparison continues until either a mismatch is found or all characters are found equal • If two strings of different lengths are compared and the comparison is equal to the last character of the shorter string • The shorter string is less than the larger string

7. string Comparison Example • Suppose we have the following declarations: • string str1 = "Hello"; • string str2 = "Hi"; • string str3 = "Air"; • string str4 = "Bill";

8. Other operators on the string Type • Binary operator + allows the string concatenation operation • For example, If str1 = "Sunny", the following statement stores the string "Sunny Day" into str2: str2 = str1 + " Day"; • The array subscript operator [] allows to access an individual character within a string • For example, If str1 = “Hello there", the following statement replaces the character t with the character T: str1[6] = ‘T’;

9. Binary operator + and array subscript operator [] – Example #include <iostream> #include <string> using namespace std; int main() { string str1, str2, str3, str4; //Line 1 str1 = "Hello There"; //Line 2 cout << "Line 3: str1 = " << str1 << endl; //Line 3 str2 = str1;//Line 4 cout << "Line 5: str2 = " << str2 << endl; //Line 5 str1 = "Sunny"; //Line 6 str2 = str1 + " Day";//Line 7 cout << "Line 8: str2 = " << str2 << endl; //Line 8 str1 = "Hello"; //Line 9 str2 = "There"; //Line 10 str3 = str1 + " " + str2;//Line 11 cout << "Line 12: str3 = " << str3 << endl; //Line 12 str3 = str1 + ' ' + str2; //Line 13 cout << "Line 14: str3 = " << str3 << endl; //Line 14 str1 = str1 + " Mickey";//Line 15 cout << "Line 16: str1 = " << str1 << endl; //Line 16 str1 = "Hello there"; //Line 17 cout << "Line 18: str1[6] = " << str1[6] << endl; //Line 18 str1[6] = 'T';//Line 19 cout << "Line 20: str1 = " << str1 << endl; //Line 20 return 0; } Output: Line 3: str1 = Hello There Line 5: str2 = Hello There Line 8: str2 = Sunny Day Line 12: str3 = Hello There Line 14: str3 = Hello There Line 16: str1 = Hello Mickey Line 18: str1[6] = t Line 20: str1 = Hello There

10. Some functions on string • length • size • find • substr • swap

11. length Function • Length returns the number of characters currently in the string • The syntax to call the length function is: strVar.length() where strVar is variable of the type string • length has no arguments • length returns an unsigned integer • The value returned can be stored in an integer variable

12. length function – Example #include <iostream> #include <string> using namespace std; int main() { string firstName; string name; firstName = "Elizabeth"; name = firstName + "Jones"; cout << firstName.length() << endl; cout << name.length() << endl; return 0; } Outputs 9 Outputs 15

13. size Function • The function size is same as the function length • Both functions return the same value • The syntax to call the function size is: strVar.size() where strVar is variable of the type string • As in the case of the function length, the function size has no arguments

14. size function – Example #include <iostream> #include <string> using namespace std; int main() { string firstName; string name; firstName = "Elizabeth"; name = firstName + "Jones"; cout << firstName.size() << endl; cout << name.size() << endl; return 0; } Outputs 9 Outputs 15

15. find Function • find searches a string for the first occurrence of a particular substring • Returns an unsigned integer value of type string::size_type giving the result of the search • The syntax to call the function find is: strVar.find(strExp) or strVar.find(strExp, pos) • where strVar is a string variable and strExp is a string expression evaluating to a string • The string expression, strExp, can also be a character • If successful, find returns the position in strVar where the match begins • For the search to be successful the match must be exact • If unsuccessful, find returns the special value string::npos (“not a position within the string”)

16. find function – Example //Example find function #include <iostream> #include <string> using namespace std; int main() { string sentence, str; //Line 1 string::size_type position; //Line 2 sentence = "Outside it is cloudy and warm."; //Line 3 str = "cloudy"; //Line 4 cout << static_cast<unsigned int> (sentence.find("is")) << endl; //Line 5 cout << static_cast<unsigned int> (sentence.find('s')) << endl; //Line 6 cout << static_cast<unsigned int> (sentence.find('o')) << endl; //Line 7 cout << static_cast<unsigned int> (sentence.find(str)) << endl; //Line 8 cout << static_cast<unsigned int> (sentence.find("the")) << endl; //Line 9 cout << static_cast<unsigned int> (sentence.find('i', 6)) << endl; //Line 10 position = sentence.find("warm"); //Line 11 cout << static_cast<unsigned int> (position) << endl;//Line 12 return 0; } Outputs 11 Outputs 3 Outputs 16 Outputs 14 Outputs 4294967295 Outputs 8 Outputs 25

17. substr Function • substr returns a particular substring of a string • The syntax to call the function substr is: strVar.substr(expr1,expr2) where expr1 and expr2 are expressions evaluating to unsigned integers • The expression expr1 specifies a position within the string (starting position of the substring) • The expression expr2 specifies the length of the substring to be returned

18. substr function – Example //Example substr function #include <iostream> #include <string> using namespace std; int main() { string sentence; //Line 1 string str; //Line 2 sentence = "It is cloudy and warm."; //Line 3 cout << sentence.substr(0, 5) << endl; //Line 4 cout << sentence.substr(6, 6) << endl; //Line 5 cout << sentence.substr(6, 16) << endl; //Line 6 cout << sentence.substr(17, 10) << endl; //Line 7 cout << sentence.substr(3, 6) << endl; //Line 8 str = sentence.substr(0, 8); //Line 9 cout << str << endl; //Line 10 str = sentence.substr(2, 10); //Line 11 cout << str << endl; //Line 12 return 0; } Outputs: It is Outputs: cloudy Outputs: cloudy and warm. Outputs: warm. Outputs: is clo Outputs: It is cl Outputs: is cloudy

19. swap Function • swap interchanges the contents of two string variables • The syntax to use the function swap is strVar1.swap(strVar2); where strVar1 and strVar2 are string variables • Suppose you have the following statements: string str1 = "Warm"; string str2 = "Cold"; • After str1.swap(str2); executes, the value of str1 is "Cold" and the value of str2 is "Warm"

20. swap function – Example //Example substr function #include <iostream> #include <string> using namespace std; int main() { string string1, string2; //Line 1 string1 = "Warm"; //Line 2 string2 = "Cold"; //Line 3 cout << "string1: " << string1 << " string2:" << string2 << endl;//Line 4 string1.swap(string2); //Line 5 cout << "string1: " << string1 << " string2:" << string2 << endl;//Line 6 return 0; }

21. End of lecture 18 Thank you!