1. Slide 1 Summary Two basic concepts: variables and assignments Some C++ practical issues: division rule, operator precedence  Sequential structure of a programme

2. Slide 2 Expression and statement An expression has a value which is the result of some operation(s) on the associated operands. 4, x-y, 2-a-(b*c) A statement is a sentence that acts as a command it does not have a value it always ends in a ‘;’ cin >> x; x = 5; int x;

3. Boolean type and expressions

4. Slide 4 Boolean type: bool  C++ contains a type (new!!!) named bool which can have one of two values * true (corresponding to non-zero value) * false (corresponding to zero value) * Boolean operators * Logical and: && * Logical or: || * Logical not: ! * Examples bool P = true; bool Q = false; bool R = true; bool S = P && Q; bool T = (!Q) || R; bool U = !(R && !Q);

5. Slide 5 How to create a boolean expression for a test? l Using relational operators l Using boolean (logical) operators An expression (a boolean expression) for a test has one of the two values: true or false.

6. Slide 6 Using Relational Operators Relational operators are used to compare two values MathC++Plain English === equals [example: if(a==b) ] [ (a=b) means put the value of b into a ] << less than  <= less than or equal to >> greater than  >= greater than or equal to  != not equal to

7. Slide 7 Relational Expressions Examples: numberOfStudents < 200 10 > 20 20 * j == 10 + i

8. Slide 8 Using Boolean (logical) operators l Logical AND operator  && l Logical OR operator  || l Logical NOT operator  ! Examples: (x>5) && (x<10) (x>10) || (x<5) !(x>5) * Warning! & and | are also operators * Boolean operators can be used to form more complex conditional expressions

9. Slide 9 Operator Precedence Which comes first? * / % + - = > == != = Answer:

10. Slide 10 Summary of Operator Precedence Precedence of operators (from highest to lowest) Parentheses ( … ) Unary operators ! Multiplicative operators * / % Additive operators + - Relational ordering = > Relational equality == != Logical and && Logical or || Assignment = arithmetic relational logical

11. Slide 11 5 != 6 || 7 <= 3 (5 !=6) || (7 <= 3) 5 * 15 + 4 == 13 && 12 < 19 || !false == 5 < 24 Example:

12. if Statements

13. Slide 13 Part I: basics

14. Slide 14 Introduction Sequence Statements in the given order Conditional statement (branching) Chooses between two (or more) sequences depending on some condition if { } else { } Iteration statement (looping) repetitively execute a given sequence while { } Three program structures or constructs:

15. Slide 15 Structured programming Any program can be written as a sequence of three basic program structures!!! 1. sequences, 2. conditionals, 3. and iterations

16. Slide 16 The fundamental if-else Statement Syntax if (Expression) Action 1 else Action 2 If Expression is true then execute Action 1 otherwise execute Action 2 Example if(v == 0) cout << "v is 0"; else cout << "v is not 0"; Expression Action 1 Action 2 true false Choose between two alternative actions depending on a test (on the values of variables).

17. Slide 17 if { } else{ } It’s common in everyday life … ?

18. Slide 18 Example: Absolute Value (1 st ) // program to read number & print its absolute value #include using namespace std; int main(){ int value; int absvalue; cout << "Enter integer: "; cin >> value; if (value < 0) absvalue = -value; else absvalue = value; cout << "The absolute value is " << absvalue << endl; return 0; }

19. Slide 19 When the action is more than one statement … Put multiple action statements within braces if { } else { }

20. Slide 20 Example: Absolute Value (2 nd ) // program to read number & print its absolute value #include using namespace std; int main(){ int value; int absvalue; // absolute value cout << "Enter integer: "; cin >> value; if (value < 0) { absvalue = -value; cout << "The input value is negative and its absolute value is " << absvalue << endl; } else { absvalue = value; cout << "The input value is positive and its absolute value is " << absvalue << endl; } return 0; }

21. Slide 21 Boolean expressions l Arithmetic expression: use arithmetic operators +,-,*,/, to produce a number as the final result l Boolean expression: use relational operators, ==, … and boolean operators AND (&&), OR (||), NOT (!) to produce one of the two values true (1) and false (0) as the final result New type: bool, true, false Example: bool cond; cond = true; cond = (x>y); … Old versions of C++, simulated boolean type by int with 0/1

22. Slide 22 Summary of if-else Statement A if (cond1) B else C D A BorC D =

23. Slide 23 Nested if-else Statements n Nested means that one complete statement is inside another if cond1 { A; if cond2 { B; } else { C } else { D }

24. Slide 24 double score; cin >> score; if(score >= 90.0) cout << "Grade = A" << endl; else if(score >= 80.0) cout << "Grade = B" << endl; else if(score >= 70.0) cout << "Grade = C" << endl; else if(score >= 60.0) cout << "Grade = D" << endl; else cout << "Grade = F" << endl; Example