1	"Brad Rippe" Brad Rippe
2	"Using Boolean Expressions" Using Boolean Expressions Multi-way Branches More about C++ Loop Statements Designing Loops
3	Questions???
4	Some Rules If both operands are type int Then the result is an int type 23 * 38 = integer result 23 / 38 = integer result If one of the operands is a double Then the result is a double type 23.56 * 38 = double result 23.56 / 38 = double result 5 / 2.0 = double result
5	Variable Types and Operations What results from the following operations? 2+2 2.0 * 4.0 3/2 3.0/2
6	Type Coercion Type Coercion: automatic conversion of an operand to another data type Promotion: convert to a higher type Demotion: convert to a lower type
7	Rules Are When operating on values of different data types, the lower one is promoted to the type of the higher one. When using the = operator, the type of expression on right will be converted to type of variable on left
8	if-else statement if(count == 1) { …do some work… } else if(count == 2) { …do some other work… } else { …do some other work… }
9	while loops while(count < 9) { … do some work… } do { …do some work… } while(count < 9);
10	while loops int count = 0; while(count < 3) { cout << “Count is “ << count << endl; count++; } cout << “I’m out!!!\n”;
11	Counter-Control Loop Count-controlled loops are those loops that are executed a fixed number of times. The number of iterations is known before commencing the loop. int i = 1; while (i <= 5) { cout << "Square of " << i; cout << " is " << (i * i); cout << endl; ++i; }
12	Sentinel-Control Loop Event-controlled loops are those loops that are executed an indefinite number of times until some condition occurs. const int SENTINEL = -1; int posInt; int sum = 0; cout << ”Enter number: \n”; cin >> posInt; while (posInt != SENTINEL) { sum += posInt; cout << “Enter number: \n”; cin >> posInt ; }
13	Pseudocode Informal language Doesn’t execute on a computer Helps with developing algorithms Described in executable statements Can be easily translated into C++
14	Pseudocode Example Prompt the user for their current salary Input the current salary Calculate the user’s retro pay for six months and output the retro pay Calculate the new annual salary and output the annual salary Calculate the new monthly salary and output the new monthly salary
15	Boolean Expressions Type bool allows declaration of variables that have a value of true or false Operators <, >, !=, ==, <=, >= &&, \|\|, ! bool executeIf = true; if(executeIf) { cout << “executed if\n”; }
16	&& - Truth tables if ( gender == 1 && age >= 65 ) seniorFemales++;
17	\|\| - Truth tables if ((semesterAverage >= 90) \|\| (finalExam >= 90)) cout << "Student grade is A" << endl;
18	Truth Table Example
19	Short Circuit Evaluations && - logical and \|\| - logical or if(x > 3 \|\| y > 3) cout << “x > 3 or y > 3” << endl;
20	bool type Evaluates to a true or false value New to C++ C uses 0 (zero) for false and a positive integer for true Side effects of C This is a compilation error in Java
21	Enums Enumerations are types with a set of integer values enum Speed { FAST, NORMAL, SLOW }; Speed speed; // expects one of the enums Enums are capitalized because they are defined a constants They are user-defined types, not given to us like int, char, double, etc.
22	Enums Can be set to explicit values or not enum Speed { FAST = 120, NORMAL = 65, SLOW = 20 }; if(speed == FAST) { // mash the pedal } else if(speed == NORMAL) { // let mom drive } else if(speed == SLOW) { // let grandma drive }
23	Blocks of Code if(freeway == 91) { // prepare to go slow } else if(freeway == 91 && day == FRIDAY) { // prepare to stop }
24	Is the following legal? int temperature = 80; if(temperature >= 100) { string msg = "Wow scorching day!\n"; } else if(temperature >= 90) { string msg = "It's a hot day!\n"; } else if(temperature >= 80) { string msg = "Not bad!\n"; } else { string msg = "Wonderful weather!\n"; } cout << msg << endl;
25	Nested if, if/else string grade; // declaration and initialization of // finalscore & midterm if (finalscore >= 90) if (midterm >= 90) grade = “A+”; else grade = “A”; else if (finalscore >= 80) grade = “B”; else if (finalscore >= 70) grade = “C”; else grade = “F”; cout << “grade= ” << grade << endl;
26	Who owns the else? if (a >= 5) { c = c + 1; if (b < 20) b = 2; } else { d = 5; } // why the second set of // {} braces if (a >= 5) c = c + 1; if (b < 20) b = 2; else d = 5;
27	Nested if, if/else string grade; // declaration and initialization of // finalscore & midterm if (finalscore >= 90) { if (midterm >= 90) { grade = “A+”; } else { grade = “A”; } } else if (finalscore >= 80) { grade = “B”; } else if (finalscore >= 70) { grade = “C”; } else { grade = “F”; } cout << “grade= ” << grade << endl;
28	Block rules
29	multi-way if/else example score = 8 gpa declared, initialized false true gpa = B display gpa as B What is advantage of the additional elses? int score = 8; char gpa = ‘ ‘; if (score >= 9) { gpa = ‘A’; } else if (score >= 8) { gpa = ‘B’; } else if (score >= 7) { gpa = ‘C’; } else { gpa = ‘F’; } cout << “grade=” << gpa; // value of gpa?
30	Multi-way if/else advantage int score = 8; char gpa = ‘ ‘; if (score >= 9) { gpa = ‘A’; } else if (score >= 8) { gpa = ‘B’; } else if (score >= 7) { gpa = ‘C’; } else { gpa = ‘F’; } cout << “grade=” << gpa; // value of gpa?
31	multi-way if/else example score = 8 gpa declared, initialized true gpa = ‘C’ skip the else block display gpa=C still WRONG int score = 8; char gpa = ‘ ‘; if (score >= 7) { gpa = ‘C’; } else if (score >= 8) { gpa = ‘B’; } else if (score >= 9) { gpa = ‘A’; } else { gpa = ‘F’; } cout << “grade=” << gpa; // value of gpa?
32	Switch Statement Syntax: switch (value) { // must be an integer result case value1: statements; … break; case valueN: statements; … break; default: statements; ... }
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34	switch statement char drink = ‘ ’; cin >> drink; switch(drink) { case 'a': price += 3.50; break; case 'b': price += 3.00; break; default : drink = 'q'; break; }
35	more switch What happens with the following code? If break statements are not used with the case statements, execution falls through to the next case
36	Break statement Used to stop execution in the current block Also used to exit a switch statement Useful to execute a single case statement without executing the statements following it Can be used to break out of loop blocks as well as switch blocks
37	switch statements Contains case labels Optional default case Similar to the if/else if statement switch(expression) { case ‘a’: break; }
38	number++ vs ++number (number++) returns the current value of number, then increments number An expression using (number++) will use the value of number BEFORE it is incremented (++number) increments number first and returns the new value of number An expression using (++number) will use the value of number AFTER it is incremented Number has the same value after either version!
39	Increment and Decrement Operators Pre-increment Operator ++a int a = 2; int b = (++a)22; Post-increment Operator a++ int a = 2; int b = (a++)22;
40	for loop structure syntax for (<initializing statement>; <continuation assertion>; <increment statement>) { <body statement>; ... <body statement>; }
41	for statement
42	For code example
43	Break and Continue break quits the loop without executing the rest of the statements in the loop. Used in switch statements Can be used in loops, but not common interrupts the current loop continue stops the execution of the current iteration and goes back to the beginning of the loop to begin the next iteration. Executes if continuation condition is true. used with loops, but not common interrupts the current loop
44	Break Example for(int i = 0; i < 10; i++) { if(i == 5) break; cout << “i is “ << i << endl; } Output: i is 0 i is 1 i is 2 i is 3 i is 4
45	Continue Example for(int i = 0; i < 10; i++) { if( i < 5 ) continue; cout << “i is “ << i << endl; } Output: i is 5 i is 6 i is 7 i is 8 i is 9
46	Nested for loop for(int j = 0; j < 5; j++) { cout << "outer: j is " << j << endl; for(int i = 0; i < 5; i++) { cout << " inner: i is " << i << endl; } }
47	What does the following output? for (int a = 1; a <= 1; a++) { cout << a++; cout << a; }
48	Debugging Loops Common errors involving loops include Off-by-one errors in which the loop executes one too many or one too few times Infinite loops usually result from a mistake in the Boolean expression that controls the loop
49	Fixing Off By One Errors Check your comparison: should it be < or <=? Check that the initialization uses the correct value Does the loop handle the zero iterations case?
50	Fix Infinite Loops Check the direction of inequalities: < or > ? Test for < or > rather than equality (= =) Check to see that you didn’t use the assignment operator (=) instead of the comparison (==)
51	Starting Over Sometimes it is more efficient to throw out a buggy program and start over The new program will be easier to read The new program is less likely to be as buggy You may develop a working program faster than if you repair the bad code The lessons learned in the buggy code will help you design a better program faster