1 COMS 261 Computer Science I Title: C++ Fundamentals Date: September 15, 2004 Lecture Number: 11

2 Announcements Read 4.1 – 4.6 Homework

3 Review Standard data types –Strings (not part of C++, but are common) –Real (float) Names Precedence

4 Outline Assignment Statement const Non-fundamental Types –string

Nonfundamental Types Nonfundamental as they are additions to the language C++ permits definition of new types and classes –A class is a special kind of type Class objects typically have –Data members that represent attributes and values –Member functions for object inspection and manipulation –Members are accessed using the selection operator j = s.size(); selection operator

Nonfundamental Types Libraries often provide special-purpose types and classes Programmers can also define their own types and classes Examples –Standard Template Library (STL) provides class string –Class string Used to represent a sequence of characters as a single object

7 Class string Some definitions string name = "Joanne"; string decimalPoint = "."; string empty = ""; string copy = name; string question = '?'; // illegal

8 Nonfundamental Types To access a library use a preprocessor directive to add its definitions to your program file #include

9 Nonfundamental Types The using statement makes syntax less clumsy –Without it std::string s = "Sharp"; std::string t = "Spiffy "; –With it using namespace std; //std contains string string s = "Sharp"; string t = "Spiffy";

10 Class string Some string member functions –size() determines number of characters in the string string Saying = "Rambling with Gambling"; cout << Saying.size() << endl; // 22 –substr() determines a substring (Note first position has index 0) string Word = Saying.substr(9, 4); // with

11 Class string –find() computes the position of a subsequence int j = Saying.find("it"); // 10 int k = Saying.find("its"); // ?

12 Class string Auxiliary functions and operators –getline() extracts the next input line string Response; cout << "Enter text: "; getline(cin, Response, '\n'); cout << "Response is \"" << Response << "\"” << endl; – Example run Enter text: Want what you do Response is "Want what you do"

13 Class string Auxiliary operators –+ string concatenation string part1 = "Me"; string part2 = " and "; string part3 = "You"; string all = part1 + part2 + part3; –+= compound concatenation assignment string thePlace = "Brooklyn"; thePlace += ", NY";

14 #include using namespace std; int main() { cout << "Enter the date in American format: " << "(e.g., January 1, 2001) : "; string Date; getline(cin, Date, '\n'); int i = Date.find(" "); string Month = Date.substr(0, i); int k = Date.find(","); string Day = Date.substr(i + 1, k - i - 1); string Year = Date.substr(k + 2, Date.size() - 1); string NewDate = Day + " " + Month + " " + Year; cout << "Original date: " << Date << endl; cout << "Converted date: " << NewDate << endl; return 0; }

15 Boolean Algebra Logical expressions have the one of two values - true or false –A rectangle has three sides –The instructor has a pleasant smile The branch of mathematics is called Boolean algebra –Developed by the British mathematician George Boole in the 19th century Three key logical operators –And, Or, Not (unary operator)

16 Boolean Algebra Truth tables –Lists all combinations of operand values and the result of the operation for each combination Example PQ P and Q False FalseFalse False TrueFalse True FalseFalse True TrueTrue

17 Boolean Algebra Or truth table Not truth table (unary operator) PQ P or Q False FalseFalse False TrueTrue True FalseTrue True TrueTrue Pnot P False True True False

18 Boolean Algebra Can create complex logical expressions by combining simple logical expressions –not (P and Q) A truth table can be used to determine when a logical expression is true PQ P and Qnot (P and Q) False FalseFalseTrue False TrueFalseTrue True FalseFalseTrue True TrueTrueFalse

19 A Boolean Type C++ contains a type named bool Type bool has two symbolic constants –true, false Boolean operators –The and operator is && –The or operator is || –The not operator is ! Warning –& and | are also operators so be careful what you type

20 A Boolean Type Example logical expressions bool p = true; bool q = false; bool r = true; bool s = (P && Q); bool t = ((!Q) || R); bool u = !(R && (!Q));

21 Relational Operators Equality operators – == – != Examples –int i = 32; –int k = 45; –bool q = (i == k); –bool r = (i != k);

22 Relational Operators Ordering operators – < – > – >= – <= Examples int i = 5; int k = 12; bool p = (i < 10); bool q = (k > i); bool r = (i >= k); bool s = (k <= 12);

23 Operator Precedence Revisited Precedence of operators (from highest to lowest) Parentheses Unary operators Multiplicative operators Additive operators Relational ordering Relational equality Logical and Logical or Assignment

24 Operator Precedence Revisited Consider 5 * == 13 && 12 < 19 || !false == 5 < 24 Yuck! Do not write expressions like this!

25 Operator Precedence Revisited Consider 5 * == 13 && 12 < 19 || !false == 5 < 24 Is equivalent to ((((5 *15) + 4) == 13) && (12 < 19)) || (!false) == (5 < 24))

26 Conditional Constructs Provide –Ability to control whether a statement list is executed Two constructs –If statement if if-else if-else-if –Switch statement Left for reading

27 The Basic If Statement Syntax if (Expression) Action If the Expression is true then execute Action Action is either a single statement or a group of statements within braces Expression Action truefalse

28 Example if (Value < 0) { Value = -Value; }

29 Sorting Two Numbers cout << "Enter two integers: "; int value1; int value2; cin >> value1 >> value2; if (value1 > value2) { int rememberValue1 = value1; value1 = value2; value2 = rememberValue1; } cout << "The input in sorted order: " << value1 << " " << value2 << endl;

30 Semantics

31 What is the Output? int m = 5; int n = 10; if (m < n) ++m; ++n; cout << " m = " << m << " n = " n << endl;

32 The If-Else Statement Syntax if (Expression) Action 1 else Action 2 If Expression is true then execute Action 1 otherwise execute Action 2 if (v == 0) { cout << "v is 0"; } else { cout << "v is not 0"; } Expression Action 1 Action 2 true false

33 Finding the Max cout << "Enter two integers: "; int value1; int value2; cin >> value1 >> value2; int max; if (value1 < value2) { max = value2; } else { max = value1; } cout << "Maximum of inputs is: " << max << endl;

34 Finding the Max

35 Selection It is often the case that depending upon the value of an expression we want to perform a particular action Two major ways of accomplishing this choice –if-else-if statement if-else statements “glued” together –Switch statement An advanced construct

36 An If-Else-If Statement if (nbr < 0){ cout << nbr << " is negative" << endl; } else if (nbr > 0) { cout << nbr << " is positive" << endl; } else { cout << nbr << " is zero" << endl; }

37 A Switch Statement switch (ch) { case 'a': case 'A': case 'e': case 'E': case 'i': case 'I': case 'o': case 'O': case 'u': case 'U': cout << ch << " is a vowel" << endl; break; default: cout << ch << " is not a vowel" << endl; }

38 cout << "Enter simple expression: "; int left; int right; char operator; cin >> left >> operator >> right; cout << left << " " << operator << " " << right << " = "; switch (Operator) { case '+' : cout << left + right << endl; break; case '-' : cout << left - right << endl; break; case '*' : cout << left * right << endl; break; case '/' : cout << left / right << endl; break; default: cout << "Illegal operation" << endl; } Example